U.S.-Mexico Water Sharing:
Background and Recent Developments
Nicole T. Carter
Specialist in Natural Resources Policy
Clare Ribando Seelke
Specialist in Latin American Affairs
Daniel T. Shedd
Legislative Attorney
January 23, 2015
Congressional Research Service
7-5700
www.crs.gov
R43312
U.S.-Mexico Water Sharing: Background and Recent Developments
Summary
The United States and Mexico share the Colorado River and Rio Grande pursuant to binational
agreements. Compliance with these agreements becomes more complicated and controversial as
water demands near or exceed available supplies and when drought and high heat further reduce
availability and increase demand.
Colorado River. The Colorado River flows through seven U.S. states before reaching Mexico,
and 97% of the basin is in the United States. A 1944 Water Treaty requires that the United States
annually provide Mexico with 1.5 million acre-feet (AF) of Colorado River water, which
represents about 10% of the river’s average flow. Binational disputes have arisen over water
quantity, quality, and conservation. Under the Treaty, disputes can be resolved through
amendments, called “minutes.” Minute 242 from 1973 requires that the salinity of Colorado River
water deliveries not exceed a specified limit. Minute 319, agreed to in 2012, provides for a
bilateral basin water management, storage, and environmental enhancement effort.
Rio Grande. The Rio Grande is governed by two separate agreements. Deliveries to Mexico in
the northwestern portion of the shared basin (near El Paso/Ciudad Juárez) occur under a 1906
Convention, while deliveries for the southeastern portion (which is below Fort Quitman, Texas)
are laid out in the 1944 Water Treaty. The 1906 Convention requires an annual delivery to Mexico
of 60,000 AF, which can be proportionally reduced based on drought conditions. The United
States is not required to make up for reduced deliveries. From 1939 to 2013, deliveries to Mexico
were reduced in roughly 30% of the years, including significant reductions in 2012, 2013, and
2014.
Under the 1944 Water Treaty, Mexico has rights to two-thirds of the flows of six Mexican Rio
Grande tributaries. The one-third delivered to the United States must average at least 350,000 AF
per year, measured in five-year cycles. The United States is entitled to all flows from U.S.
tributaries. Mexico met its delivery obligations until the region’s 1994-2003 drought.
The current five-year cycle will end in October 2015. Water accounting for the basin has been
receiving considerable attention since the second year of the current five-year cycle (October
2011 to October 2012), when Mexico’s deliveries were less than 30% of the target. The dry
conditions in the basin at that time raised tensions as water constraints intensified. As of late
January 2015, Mexico remained behind on its deliveries for the current five-year cycle, although
the extent and intensity of the basin’s dry conditions had significantly diminished.
The International Boundary and Water Commission (IBWC) is the entity charged with providing
binational solutions to issues that arise during application of the water-sharing treaties. Since late
2012, the Mexican and U.S. Sections of the IBWC have been regularly meeting to discuss
Mexico’s water deliveries and various water accounting concerns.
Legislative Responses. Some Members of Congress have expressed concerns about the adequacy
of Mexico’s 1944 Water Treaty compliance, U.S. efforts to hold Mexico to its treaty obligations,
and the resulting economic impacts, especially in Texas border counties. On December 16, 2014,
P.L. 113-235, the Consolidated and Further Continuing Appropriations Act, 2015, became law,
and a provision in this omnibus legislation required that the U.S. Section of the IBWC report to
the Committees on Appropriations on various water delivery and accounting issues within 45
days of enactment.
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U.S.-Mexico Water Sharing: Background and Recent Developments
Contents
U.S.-Mexico Water Sharing ............................................................................................................. 1
1944 Water Treaty ............................................................................................................................ 3
Responsibilities, Execution, and Treaty Minutes ...................................................................... 3
Water Distribution Requirements .............................................................................................. 4
Other Treaty Provisions ............................................................................................................. 6
Drought Conditions ......................................................................................................................... 7
Colorado River Basin ...................................................................................................................... 9
Salinity ....................................................................................................................................... 9
Instream Flows for Environmental Protection ......................................................................... 10
Minute 319: Water Conservation and Environmental Protection ............................................ 10
Rio Grande Basin ........................................................................................................................... 11
Northwestern Rio Grande Basin (El Paso-Ciudad Juárez) ...................................................... 11
Southeastern Rio Grande Basin (below Fort Quitman, Texas) ................................................ 12
Mexico’s Rio Grande Deliveries ....................................................................................... 13
An Over-Allocated Basin .................................................................................................. 14
Responses to Mexico’s Rio Grande Water Delivery Shortfalls ..................................................... 15
Stakeholder Perspectives ......................................................................................................... 15
Diplomatic Responses ............................................................................................................. 16
Congressional Responses ........................................................................................................ 17
Figures
Figure 1. Illustration of Colorado River Basin ................................................................................ 2
Figure 2. Illustration of Rio Grande Basin....................................................................................... 3
Figure 3. Evolution of North American Drought from 2011 to 2014 .............................................. 8
Figure 4. Estimated Mexican Deliveries to United States, October 2010 to October 2015
Cycle, Under 1944 Water Treaty ................................................................................................ 14
Contacts
Author Contact Information........................................................................................................... 18
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U.S.-Mexico Water Sharing: Background and Recent Developments
U.S.-Mexico Water Sharing
How to share water has long been a complex issue for the U.S.-Mexico border region and in the
broader U.S.-Mexico relationship.1 The two countries share a nearly 2,000-mile border. Multiple
rivers cross the border or form the border at various points. The principal shared river basins are:
• the Colorado River, which is predominantly in the United States, and crosses the
Mexican border on its way to the Gulf of California (Figure 1), and
• the Rio Grande, with major tributaries in the United States and Mexico and
whose riverbed is the U.S.-Mexico border in Texas (Figure 2).
In the 19th century, numerous questions arose regarding the boundaries between the two countries
and water sharing of international rivers. Early agreements, starting in 1848, sought to clarify the
location of the border.2 Later in the century, the two countries entered into the Convention of
March 1, 1889, establishing the International Boundary Commission (IBC) to apply border
agreements.3 Starting in 1906, agreements to distribute water binationally began to emerge; a
1906 convention on the sharing of Rio Grande for irrigation purposes distributed water in the
vicinity of El Paso, Texas.4 In 1944, the two countries entered into a treaty on “Utilization of
Waters of the Colorado and Tijuana Rivers and of the Rio Grande” (hereinafter Treaty or 1944
Water Treaty).5 The Treaty reconfigured the IBC into the International Boundary and Water
Commission (IBWC), which provides binational support and facilitates resolution of issues
arising during application of U.S.-Mexico treaties on water quantity, sanitation, water quality,
flood control, and boundary demarcation.
This report is a primer on U.S. and Mexican water-sharing topics. It focuses on surface water
quantity sharing and recent developments, including drought conditions. Due to Mexico’s recent
below-target deliveries of Rio Grande water to the United States, particular attention is given to
the status, underlying causes, and responses to the Rio Grande water delivery shortfalls. This
report describes:
• legal obligations and processes under the 1944 Water Treaty;
• drought conditions from 2010 to 2013;
• water sharing and developments in the Colorado River Basin;
1 For background on the broader U.S.-Mexican relationship, see CRS Report R42917, Mexico: Background and U.S.
Relations, by Clare Ribando Seelkehttp://www.crs.gov/pages/Reports.aspx?PRODCODE=R42917.
2 Treaty of Guadalupe Hidalgo, U.S.-Mex., February 2, 1848, available at http://www.ibwc.state.gov/Files/
Treaty_of_1848.pdf (ending the Mexican-American War).
3 Convention Between the United States and Mexico regarding the Water Boundary, U.S.-Mex., December 2, 1898,
available at http://www.ibwc.state.gov/Files/TREATY_OF_1889.pdf.
4 Convention of May 21, 1906, on the Equitable Distribution of the Waters of the Rio Grande, available at
http://www.ibwc.gov/Files/1906Conv.pdf.
5 Treaty between the United States of America and Mexico Respecting Utilization of Waters of the Colorado and
Tijuana Rivers and of the Rio Grande, U.S.-Mex., Feb. 3, 1944, 59 Stat. 1219 (hereinafter referred to as the 1944 Water
Treaty or the Treaty).
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• water sharing in the Rio Grande Basin and Mexico’s water delivery shortfalls;
and
• stakeholder, diplomatic, and legislative responses to the rate of Mexico’s Rio
Grande water deliveries.
Figure 1. Illustration of Colorado River Basin
Source: The Earth Institute at Columbia University (with minor modification by CRS), at
http://blogs.ei.columbia.edu/wp-content/uploads/2012/12/CO-River-Basin-REVISED.jpg, and modified by CRS.
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Figure 2. Illustration of Rio Grande Basin
Source: New Mexico Museum of Natural History and Science, at http://www.nmnaturalhistory.org/BEG/
BEG%20Images/MAP_RGB_pg48.jpg, and modified by CRS.
1944 Water Treaty
Responsibilities, Execution, and Treaty Minutes
The 1944 Water Treaty establishes water allocations for the United States and Mexico and creates
the current governance framework for the IBWC to resolve disputes arising from its execution.6
The IBWC is an international body consisting of U.S. and Mexican Sections, which are overseen
by the State Department and the Mexico Ministry of Foreign Relations, respectively.7 Any
6 Ibid.
7 Ibid. The members of the IBWC are granted diplomatic status and enjoy “the privileges and immunities appertaining
(continued...)
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disputes that arise under the 1944 Water Treaty are settled through the Treaty’s “minute” process.
The IBWC is authorized to develop rules and to issue decisions regarding the execution of the
Treaty in the form of minutes,8 which become legally enforceable and essentially amend the
Treaty. A proposed minute is forwarded within three days to the government of each country for
approval.9 If the government of either country fails to announce its approval or disapproval within
30 days, the minute is considered approved.10 If either government disapproves, the matter is
removed from IBWC control and the two governments negotiate the issue.11 If an agreement is
reached between the governments, the IBWC must then take any further actions “as may be
necessary to carry out such agreement.”12 For the United States, the executive branch has the
authority to approve or disapprove of the proposed minutes arising from the Treaty;13 the
President only has the ability to make such agreements pursuant to a treaty if the agreement is in
the purview of the treaty.14
Water Distribution Requirements
The basic water distribution arrangements in the 1944 Water Treaty are as follows.
• For the Colorado River basin, the United States is to provide Mexico annually
with 1.5 million acre-feet (AF)15 of water.16
• For the Rio Grande basin below Fort Quitman, Texas,
—Mexico has the rights to two-thirds of the flows that feed into the Rio Grande from the
six major tributaries that enter from Mexico: the Conchos, San Diego, San Rodrigo,
Escondido, and Salado Rivers and the Las Vacas Arroyo (stream).17
(...continued)
to diplomatic officers” and may “freely carry out their observations, studies and field work in the territory of either
country” (ibid.). However, all works and structures that are wholly located within one country—despite the potential
international character of such works—remain under the exclusive jurisdiction of the country in which they are located.
Each country is responsible for the expenses incurred by their respective section; however, joint expenses are “borne
equally by the two Governments.” The U.S. Section of the IBWC is typically funded through the annual State
Department and Foreign Operations appropriations bill.
8 Ibid., art. 25.
9 Ibid.
10 Ibid.
11 Ibid.
12 Ibid.
13 The Administration has authority to agree to the minutes because they are agreements made pursuant to the 1944
Water Treaty, a treaty that the Senate has ratified. Because a properly enacted treaty is the “Supreme Law of the Land,”
the power to enter into an agreement required or contemplated by the treaty lies fairly clearly within the President’s
executive function. U.S. Const. art. VI, § 2 (“the laws of the United States ... [and] all treaties made, or which shall be
made, under the authority of the United States, shall be the supreme Law of the Land.”); Congressional Research
Service, Treaties and Other International Agreements: The Role of the United States Senate, A Study Prepared for the
Senate Comm. on Foreign Relations 5 (Comm. Print 2001). For further discussion on the treaty process and executive
agreements, see CRS Report RL32528, International Law and Agreements: Their Effect upon U.S. Law, by Michael
John Garcia.
14 Ibid., art. 26.
15 An acre-foot is about 326,000 gallons of water, enough to cover an acre of land with one foot of water.
16 Treaty, art. 10.
17 Ibid., art. 4(A)(c).
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—the United States receives all flows from Rio Grande tributaries in the United States
and one-third of flows from the six Mexican tributaries.18 Mexico’s water delivery
from these six tributaries must average at least 350,000 AF per year, measured in five-
year cycles.19
If Mexico fails to meet its minimum flow obligations for a five-year cycle because of
“extraordinary drought”—a term not defined in the 1944 Water Treaty—it must make up the
deficiency during the next five-year cycle with water from the Mexican tributaries.20 Minute 234
established that Mexico may repay a water debt using three sources of water: (1) excess water
from its tributaries; (2) a portion of its allotment from its tributaries; or (3) a transfer of its stored
water in the international reservoirs.21
If Mexico fails to meet its minimum flow obligations for a five-year cycle and there is no
agreement that an extraordinary drought existed, Article 24(d) of the 1944 Water Treaty provides
certain mechanisms for dispute settlement. First, the IBWC has the authority “to settle all
differences that may arise between the two Governments with respect to ... application of the
Treaty.”22 However, if the commissioners are unable to reach agreement on a dispute, the dispute
shall be settled through diplomatic channels between the United States and Mexico.23 Article 24
also provides that the countries may seek recourse in any “general or special agreements which
the two Governments have concluded for the settlement of controversies.”24 However, it does not
appear that these mechanisms have been necessary in the past. As discussed throughout this
report, the United States and Mexico previously have used the minute process and diplomatic
efforts to reconcile disputes regarding the 1944 Treaty.
Article 9 of the 1944 Water Treaty provides the IBWC with some flexibility regarding the
diversion of water from the Rio Grande. For example, in cases of extraordinary drought occurring
in one of the countries, the IBWC may permit water to be withdrawn from the other country in
order to help alleviate drought conditions.25 Further, the IBWC may allow one country to use
water allocated to the other country if it can be done “without injury to the latter and can be
replaced at some other point on the river.”26 However, if the IBWC authorizes temporary
diversions of water from one country to another, the use of such water does not establish a
permanent right to divert.27 Under article 9, the IBWC also is responsible for keeping records
concerning the water belonging to both Mexico and the United States.
The 1944 Water Treaty establishes a hierarchy of uses for the water: (1) domestic and municipal
uses; (2) agriculture and stock-raising; (3) electric power; (4) other industrial uses; (5) navigation;
18 Ibid., art. 4(B).
19 Ibid., art. 4(B)(c).
20 Ibid., art. 4. For more on compliance, see Allie Alexis Umoff, “An Analysis of the 1944 U.S.-Mexico Water Treaty:
Its Past, Present, and Future,” Environs: U.C. Davis School of Law Environmental Law and Policy Journal, vol. 32, no.
1 (2008), hereinafter Umoff 2008.
21 IBWC Minute 234, December 2, 1969.
22 Treaty, art. 24(d).
23 Ibid.
24 Ibid.
25 Ibid., art. 9(f).
26 Ibid., art. 9(d).
27 Ibid., art. 9(e).
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(6) fishing and hunting; and (7) any other beneficial uses which may be determined by the
Commission.28 A frequent critique of this hierarchy is that it does not include an obligation to
maintain water for ecological purposes.29 In addition, the original 1944 Treaty does not have any
provisions that establish requirements for water quality, but only establishes the quantity
requirements outlined above.30 This led to tensions regarding salinity levels in the United States
deliveries to Mexico after the 1944 Treaty was ratified.31 As discussed in the “Salinity” section
below, the two countries agreed to Minute 242 in 1973 to resolve the dispute.32
Regarding management of reservoirs in the basin that are wholly in one country, the Protocol
accompanying the original 1944 Water Treaty establishes that constructed works, such as dams
and conveyance structures, in one country that are used only partly for Treaty compliance shall be
constructed and operated by the federal agencies of that country, in conformance with the Treaty
and in cooperation with IBWC.33 Subsequent minutes, like Minute 319 (which is discussed below
in “Minute 319: Water Conservation and Environmental Protection”), have integrated operational
activities in specific circumstances for specific works. To what extent Mexico is operating its
reservoirs to support Treaty compliance or prioritizing domestic water demands is a point of
debate discussed in the “Stakeholder Perspectives” section below, which focuses on Mexico’s Rio
Grande water delivery shortfalls.
Other Treaty Provisions
The 1944 Water Treaty established other requirements beyond water distribution obligations. The
Treaty, among other things, (1) provided for the construction of certain dams and channels along
the rivers;34 (2) required the IBWC to establish studies and prepare plans for flood control;35
(3) provided that the IBWC should study and plan for the generation of hydroelectric energy
along the rivers;36 and (4) required the IBWC to establish regulations for the maintenance and
operation of reservoirs.37 Discussion of these treaty requirements is beyond the scope of this
report.
28 Ibid., art. 3.
29 See, for example, Umoff 2008.
30 See Treaty.
31 See Umoff 2008, p. 78.
32 IBWC Minute 242, Aug 30, 1973.
33 The Protocol states that for “construction or use of works for storage or conveyance of water, flood control, stream
gaging, or for any other purpose, which are situated wholly within the territory of the country of that Section, and
which are to be used only partly for the performance of treaty provisions, such jurisdiction shall be exercised, and such
functions, including the construction, operation and maintenance of the said works, shall be performed and carried out
by the Federal agencies of that country which now or hereafter may be authorized by domestic law to construct, or to
operate and maintain, such works. Such functions or jurisdictions shall be exercised in conformity with the provisions
of the Treaty and in cooperation with the respective Section of the Commission, to the end that all international
obligations and functions may be coordinated and fulfilled.” Treaty, Protocol.
34 Treaty, art. 5.
35 Ibid., art. 6.
36 Ibid., art. 7.
37 Ibid., art. 8.
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Border Aquifers Are Largely Not Addressed by Binational Agreements
Binational aquifers also are shared water resources that can be particularly important for meeting needs during dry
times; roughly 20 binational aquifers are significant sources of domestic water supply for overlying populations. For
example, the Hueco Bolson aquifer provides Ciudad Juárez’s 1.5 mil ion residents and two-fifths of El Paso’s 730,000
residents with water.
Many border aquifers have experienced significant declines in volume and/or quality. No broad bilateral agreement
exists on U.S.-Mexico border groundwater management and use. Declining water levels, deteriorating water quality,
and increasing use of groundwater resources have raised concerns about the long-term availability of the border’s
aquifers. Knowledge about the extent, depletion rates, and quality of transboundary aquifers is limited and in some
areas completely absent. A binational aquifer quantity and quality assessment has been initiated, pursuant to the U.S.-
Mexico Transboundary Aquifer Assessment Act (P.L. 109-448). The act authorized the Secretary of the Interior,
through the U.S. Geological Survey (USGS), to col aborate with the States of Arizona, New Mexico, and Texas
through their Water Resources Research Institutes (WRRIs) and with the International Boundary and Water
Commission, stakeholders, and Mexican counterparts to provide information and a scientific foundation for state and
local officials to address pressing challenges along the U.S.-Mexico border. According to the act’s accompanying
Senate report (S.Rept. 109-17):
Ground-water pumping has lowered the water table, depleted aquifers, and reduced the base flow of
many streams thus decreasing the quantity of water available to support critical riparian habitats.
Excessive ground-water pumping in some major urban centers, such as in the El Paso/Juarez
metropolitan region, has caused land subsidence that has damaged homes and essential urban
infrastructure. In addition to the effects of ground- and surface-water depletion, degradation of water
quality has reduced habitat suitability for the region's diverse biota.
The assessment was authorized in 2006 for $50 million. The USGS used and distributed a total of $2 million through
FY2010 for the assessment. It has received no subsequent funding as of November 2013. Mexico also contributed
funding, but estimated funding levels are not available. Additional USGS-supported work is contingent on funding.
Sources: G. E. Eckstein, “Buried Treasure or Buried Hope? The Status of Mexico-U.S. Transboundary Aquifers under
International Law," International Community Law Review, vol. 13 (2011), pp. 273-290; W. A. Al ey, Five-Year Interim
Report of the United States-Mexico Transboundary Aquifer Assessment Program: 2007 -2012, U.S. Geological Survey, Open
File Report 2013-1059, Reston, VA, 2013; Christopher E. Wilson, Erik Lee, et al., The State of the Border Report: A
Comprehensive Analysis of the U.S.-Mexico Border, Woodrow Wilson Center, El Colegio de la Frontera Norte, Arizona
State University, May 2013.
Drought Conditions
Water sharing becomes more complicated during droughts, and both the Colorado River and the
Rio Grande basins are prone to multiyear droughts. For the Rio Grande, as shown in Figure 3,
both 2011 and 2012 were marked by dry conditions, resulting from high heat, low precipitation,
and low runoff throughout most of the basin. For the Colorado River, dry conditions developed
more noticeably in 2012 and persisted in 2013 and 2014, with dry conditions intensifying in some
portions of the basin. Significant rains in late August and September 2013 in some parts of the
basin provided some relief, but also resulted in significant flooding and damage, particularly in
the state of Colorado.38
38 For more on the causes and consequences of drought, see CRS Report R43407, Drought in the United States: Causes
and Current Understanding, by Peter Folger and Betsy A. Cody.
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Figure 3. Evolution of North American Drought from 2011 to 2014
Source: North American Drought Monitor maps (minor modifications by CRS), available at
http://www.ncdc.noaa.gov/temp-and-precip/drought/nadm/nadm-maps.php. These maps are created by U.S.,
Mexican, and Canadian experts who synthesize various drought indices and impacts.
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Colorado River Basin
As depicted in Figure 1, the Colorado River flows through seven U.S. states (Arizona, California,
Colorado, Nevada, New Mexico, Utah, and Wyoming) and forms the border between the Mexican
states of Baja California Norte and Sonora, before emptying into the Gulf of California; 97% of
the basin is in the United States. Disputes have erupted over the use of the Colorado River water
supplies for most of the past century. Although many of these disputes have related to state
allocations on the U.S. side of the border, issues have also arisen over water quality, availability,
and conservation between the United States and Mexico.
When the 1944 Water Treaty was signed, Colorado River flows were estimated at some 16.8
million AF per year. Current flows are now likely closer to 14.4 million AF annually.39 That is,
the 1944 Treaty requirement that the United States provide Mexico with 1.5 million AF annually
means that the United States retains roughly 90% of the average flow, but less than originally
estimated. In December 2012, the Department of the Interior’s Bureau of Reclamation published
a study documenting that the demand for the basin’s water in the United States in some years
exceeds supply, and that the demand-supply imbalance is anticipated to worsen in coming
decades.40 While discussion of Colorado River water issues within the United States is beyond the
scope of this report, concern about meeting future demands in the United States is significant to
the context of discussions about the basin’s water sharing with Mexico.
The following treaty implementation issues in the Colorado River basin are discussed in more
detail below: salinity, environmental protection, and Minute 319.
Salinity
While the United States has consistently delivered Mexico’s minimum allotment of Colorado
River water, disputes did arise about the quality of the water. In the 1960s, salinity in the
Colorado River rose dramatically.41 Mexico was receiving water that was too salty for human,
livestock, or agricultural uses. The IBWC helped both countries agree to Minute 218, which took
effect in 1965 for a period of five years, requiring the United States to extend a drainage channel
to reduce salinity. Five years later, Mexican farmers remained angry about the salinity issue. After
the Mexican government threatened to take the water dispute to the International Court of Justice,
the United States agreed to Minute 242 in 1973. Per Minute 242, the United States agreed to
construct additional channels to control salinity, fund clean-up of the Mexicali Valley lands
damaged by the accumulation of salts, and keep salinity levels of delivered water below a certain
level. Minute 242 remains in force, and the United States continues to comply with its provisions.
39 “U.S., Mexico: The Decline of the Colorado River,” Stratfor Global Intelligence, May 13, 2013.
40 U.S. Dept. of the Interior, Bureau of Reclamation, Colorado River Basin Water Supply and Demand Study,
December 2012.
41 Part of the U.S. effort to manage the salinity of its water included the construction of the Yuma Desalting Plant by
the Department of the Interior’s Bureau of Reclamation. This facility has rarely operated since its construction,
however, due in part to the cost of its operations (desalination can require considerable electricity to operate). Instead,
the high-saline irrigation water has been disposed (through a canal that enters Mexico and discharges into wetlands
called the Ciénega de Santa Clara near the Gulf of California) separately from the United States’ required deliveries to
Mexico. Whether and how the Yuma Desalting facility should be operated, and how the impacts on the Ciénega de
Santa Clara from the reduced discharge of the untreated irrigation runoff should be managed, remain topics of some
debate in the basin.
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While the IBWC-backed resolution to this crisis proved to be successful, the agreement took a
long time and required external pressure to be reached.42
Instream Flows for Environmental Protection
The Colorado River Delta at the terminus of the Colorado River, prior to significant expansion of
the basin’s water consumption, covered 9,650 square miles in the United States and Mexico. The
Mexican side of the delta contains wetlands, woodlands and desert areas that are home to many
endangered species; part of Mexico’s delta is a designated United Nations Biosphere Reserve.
According to environmental interests, insufficient water flowing into the delta has contributed to
the degradation of 90% of the delta’s wetlands;43 these interests recommend that annual flows
accompanied by larger pulses of water every four years would restore the wetlands.44 These
stakeholders have argued that “environmental protection” should be added to the 1944 Treaty as a
factor in determining water deliveries to Mexico. Other stakeholders are less supportive of these
restoration efforts; some are concerned that they may reduce the allocations available for U.S.
users and others do not want to support these efforts while the question of Mexico’s compliance
with water deliveries in the Rio Grande basin is raising tensions (discussed in “Responses to
Mexico’s Rio Grande Water Delivery Shortfalls”).
The issue of instream flows for environmental protection entered bilateral discussions in the
IBWC in the late 1990s. In recent years, bilateral discussions in the basin coalesced around
improved management of and conservation of both the Colorado River and its delta. Both
governments, along with state officials and conservation groups, worked with the IBWC to
develop an agreement that would allocate water to Mexico based on whether there was a surplus
or drought and allow for joint investments to create greater environmental protection, as well as
greater water conservation (i.e., ability to store water) for Mexico. These discussions led to
Minute 319.
Minute 319: Water Conservation and Environmental Protection
Minute 319 was signed on November 20, 2012, and is to be enforced for five years (with the
possibility of an extension through 2026 if not supplanted or replaced by another minute). Some
view Minute 319 as a step forward in bilateral water management and environmental protection
efforts.45 Others do not support Minute 319 for a variety of reasons, including that the minute
signaled increasing cooperation at the same time that water tensions in the Rio Grande basin were
particularly acute.
Key elements of the agreement include:
• extending provisions of Minute 318 (Cooperative Measures to Address the
Continued Effects of the April 2010 Earthquake in the Mexicali Valley, Baja,
California), to allow Mexico to defer delivery of its Colorado River water
allocation while Mexico repairs earthquake-damaged infrastructure;
42 Umoff 2008.
43 CRS phone interview with Carlos de la Parra, Professor at El Colegio de la Frontera Norte, Mexico, July 8, 2013.
44 Sierra Club, Regional Conservation Committee: Colorado River Report, February 2001.
45 CRS phone interview with Carlos de la Parra, Professor at El Colegio de la Frontera Norte, Mexico, July 8, 2013.
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• delivering additional water (i.e., above the 1.5 million AF annual delivery
required by the Treaty) to Mexico when water levels are high in Lake Mead;
• reducing deliveries during low Lake Mead reservoir conditions (i.e., Mexico’s
annual water deliveries would be reduced by up to 0.5 million AF, similar to the
reduction by the U.S. lower basin states);46
• implementing jointly funded water efficiency and conservation projects to free up
water for the Colorado River Delta;
• creating a mechanism by which U.S. water deliveries to Mexico can be held in
United States reservoirs for subsequent delivery; and
• continuing to work together to address salinity concerns per Minute 242.
Rio Grande Basin
On most maps, the Rio Grande appears as a continuous line from Colorado to the Gulf of Mexico;
in reality, the river dries up at various points. Consequently, what looks like a continuous basin in
Figure 2 actually operates as separate binational basins divided into:
• the northwestern El Paso-Juárez Rio Grande basin from south of Elephant Butte
Dam in New Mexico past the water withdrawals and return flows of El Paso,
Texas, and Ciudad Juárez, Chihuahua; and
• the southeastern Lower Rio Grande basin, including its tributaries (e.g., Rio
Conchos) from Fort Quitman, Texas, to the Gulf of Mexico.
Binational water sharing agreements differ in the two binational Rio Grande basins. In the
northwestern El Paso-Juárez basin, the United States is required to deliver water to Mexico. In the
southeastern Lower Rio Grande basin, it is largely Mexico that is obligated to deliver water to the
United States. A common characteristic of both basins is that the water demands regularly exceed
supply; this imbalance becomes particularly apparent during droughts. While the northwestern El
Paso-Juárez water issues have raised significant local concerns recently, the delivery of water
from Mexico in the southeastern Rio Grande basin has received the majority of national media
and political attention.
Northwestern Rio Grande Basin (El Paso-Ciudad Juárez)
Under the 1906 Convention that guides U.S. deliveries to Mexico at Ciudad Juárez, the United
States is to deliver to Mexico 60,000 AF (enough water to irrigate about 25,000 acres) for use in
the Juárez Valley of Chihuahua. However, during conditions of extraordinary drought, these
deliveries to Mexico are reduced proportionally to reductions in available supplies in the broader
basin. From 1939 to 2014, deliveries to Mexico were reduced in roughly 30% of the years; the
United States is not required to repay any reduced deliveries. For example, in 2012, U.S.
46 Minute 319 stipulates: “the Government of the United States will provide the most current information to Mexico on
basin conditions as often as required, including precipitation, stream flow, and water storage conditions in the basin and
their historical behavior; the consumptive water uses for the different basin states, and the historical trend; and the
status of the determination of shortage conditions in the Colorado River Basin within the United States ...” This level of
data sharing is higher than required in the Rio Grande basin.
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deliveries to Mexico were curtailed, due to drought, to an estimated 23,200 AF (39% of full
allotment). In 2013, U.S. deliveries to Mexico were estimated at 3,700 AF (6% of full allotment),
and in 2014, the estimated delivery to Mexico was 18,300 (30% of full allotment).
In recent years, U.S. water deliveries to Mexico in the northwestern binational Rio Grande basin
have drawn regional attention because the Middle Rio Grande (the portion of the river that
traverses New Mexico) has experienced particularly low flow conditions and low storage at
reservoirs due to drought. Junior water rights holders (whose water allocations are reduced prior
to those with more senior rights) in New Mexico and Texas have received deeply curtailed
deliveries (as low as 4% of a full allotment) in recent years.
Specifically, U.S. stakeholders associated with the U.S. Bureau of Reclamation’s Rio Grande
Project are interested in how water is being delivered to Mexico when the basin is affected by
drought. The Rio Grande Project furnishes irrigation water for approximately 178,000 acres in
New Mexico and Texas, as well as electric power. Water deliveries from this project have been
significantly curtailed as multiple years of dry conditions have depleted reservoir storage.
In particular, the timing of the water releases in 2012 for delivery to Mexico and their potential
impacts on U.S. regional interests (e.g., potential conveyance losses because releases for Mexico
would not be timed with deliveries to U.S. water districts) raised concerns among some U.S.
stakeholders.47 Mexican growers had sought the surface water deliveries because pumping
problems had impaired their ability to start the agricultural season using groundwater.
Southeastern Rio Grande Basin (below Fort Quitman, Texas)
In the southeastern Lower Rio Grande basin, Mexico is required to deliver water to the United
States under the 1944 Treaty. As previously noted, the southeastern Lower Rio Grande water
delivery account is managed largely on five-year cycles. Mexico’s compliance with Treaty
delivery requirements often has been accomplished through wet weather flows, rather than
purposeful releases from Mexican reservoirs during dry conditions.
Mexico met its deliveries within the five-year cycles until the 1994-2003 drought.48 During that
drought period Mexico accrued a water debt through two five-year water cycles.49 Diffusion of
47 Letter from Patrick R. Gordon, Texas Commissioner, Rio Grande Compact Commission, to Edward Drusina,
Commissioner, U.S. Section, International Boundary and Water Commission, April 9, 2012; Texas Agrilife Research
Center, Drought Watch, February 2013.
48 During the two five-year cycles between 1992 and 2002, Mexico incurred water debt, failing to deliver the 1,750,000
AF (average annual 350,000 AF) required under the Treaty. See Umoff, 2008. In Minute 293 from October 1995, the
United States agreed to loan Mexico water to alleviate the drought. However, in subsequent years Mexico’s water debt
continued to increase. Minute 308, from June 2002, required Mexico to immediately transfer 90,000 AF of water from
international reservoirs to the United States, as partial repayment of the water debt, and required Mexico to conduct
studies to improve drought management. After extended negotiations, the two countries reached a solution to eliminate
Mexico’s water debt for the aforementioned shortages in 2005.
49 As previously noted, Minute 234, established in 1969, includes a procedure whereby Mexico may pay a water debt
using three different sources of water. Minute 234 requires that the deficit payments from these three sources be made
concurrently with required deliveries in the following five-year cycle. The United States and Mexico differ in their
interpretation and implementation of Minute 234. For example, Mexico claimed that in the event of extraordinary
drought, only the deficit incurred during the 1992-1997 five-year water cycle needed to be repaid in the following five-
year cycle (i.e., by 2002), and any deficit incurred during the 1997-2002 cycle could be deferred until the next five-year
cycle. The United States argued that Minute 234 required that the water debt incurred during the 1997-2002 cycle be
(continued...)
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tensions over the debt was accomplished through presidential intervention, negotiation of new
minutes under the 1944 Treaty, and investments in improved water efficiency. Hurricane-induced
wet conditions cleared the remaining water debt in 2005.50 The most significant tributary in the
southeastern Rio Grande basin is Mexico’s Rio Conchos, which historically contributed 70% of
the flow in the Rio Grande, but as of the 1990s was only contributing 40% of the flow. Significant
irrigated agricultural production developed in the Rio Conchos basin during the 1980s and early
1990s. It is the change in water deliveries from the Rio Conchos that garnered most of the critical
attention during the 1994-2003 drought.
Mexico’s Rio Grande Deliveries
The current delivery cycle started October 25, 2010, and is anticipated to end October 24, 2015.
In October 2014, at the end of the fourth year of the five-year cycle, Mexico was roughly 339,495
AF (24%) behind in deliveries, based on a total target delivery for those four years of 1,400,000
AF, as shown in Figure 4.51 Although these figures were published by IBWC’s U.S Section,
adjustments to the agreed-upon water accounting under the treaty may be made subsequent to the
release of these delivery figures.
A significant cause of the missed target delivery stems from a deficit of more than 249,000 AF of
the annual 350,000 AF target that occurred during the second year of the cycle—that is, deliveries
from Mexico were less than 30% of the annual target from October 2011 to October 2012. In the
third year of the cycle, Mexico is estimated to have exceeded the target delivery, with roughly
374,000 AF delivered to the United States. In the fourth year of the cycle, available estimates
indicate that Mexico delivered less than target annual average allotment.
The timing of the Mexican deliveries within the five-year cycle is a point of tension among some
basin interests. This tension was particularly acute during 2012, which falls largely within the
second year of the cycle shown in Figure 4, as Texas water rights holders faced persistent dry
conditions and Mexican water deliveries were below the target deliveries. Two binational
reservoirs on the Rio Grande store much of the water Mexico delivers to the United States; these
reservoir releases help regulate when the water is delivered to U.S. interests, thereby increasing
the value of the delivered water in meeting U.S. water demands. Some U.S. stakeholders argue
that the uncertainty regarding the timing of Mexico’s deliveries reduces the effective utilization
and management of the delivered water, its storage, and its release. Mexico, on the other hand,
argues that its deliveries are in compliance with the cycle provided for in the 1944 Water Treaty.
(...continued)
made up concurrently with the 1992-1997 water debt. The matter was left unresolved.
50 C. Reed, “The Texas-Mexico Water Dispute and Its Resolution (?): Agricultural Liquid & Land Practice and
Discourse along the Rio Conchos, Chihuahua, 1990-2005,” (Ph.D. dissertation, The University of Texas at Austin,
2007); hereinafter Reed 2007. For additional information, see footnote 48 of this report.
51 For the 1992 to 1997 cycle, Mexico’s water debt was roughly 1 million AF, which is carried over into the next cycle
under the extraordinary drought provision of the 1944 Water Treaty. At the end of the 1997 to 2002 cycle, the debt had
grown to roughly 1.5 million AF.
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Figure 4. Estimated Mexican Deliveries to United States,
October 2010 to October 2015 Cycle, Under 1944 Water Treaty
Source: CRS, adapted from IBWC U.S. Section data. Figure shows estimated volumes delivered to the U.S.
from six Mexican tributaries named in the 1944 Water Treaty.
An Over-Allocated Basin
Demands for water in the southeastern Rio Grande basin exceed average supply; it is an over-
allocated basin. This imbalance became acute during the 1994-2003 drought. During that drought,
the water supply for U.S. agriculture in the Lower Rio Grande basin averaged 78% of the full
allocation from 1994 to 1996, and 53% from 1997 to 2004.52 Currently, Texas water users other
than priority water users (i.e., municipal, domestic, and industrial users) can expect to receive on
average 70% of their water allocation in average water years.53
Over-allocation in Mexico’s Rio Grande basin also exists.54 Much of Mexico’s over-allocation is
attributed to the expansion of Mexican irrigated agriculture from 1965 to 1994, first in
52S. Sandoval-Solis, “Water Planning and Management for Large Scale River Basin Case of Study: the Rio Grande/Rio
Bravo Transboundary Basin”, (Ph.D. dissertation, The University of Texas at Austin, 2011). Hereinafter Sandoval-
Solis 2011.
53 Sandoval-Solis 2011.
54 Sandoval-Solis 2011.
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Tamaulipas and later in Chihuahua. Significantly, Texas agricultural water withdrawals did not
increase at a similar rate during this period in part because agriculture was already well
established on the U.S. side of the border. Growth in industrial activity near the border associated
largely with the maquiladora (export assembly plant) industry in Mexico and population growth
in the basin’s urban areas on both sides of the border also increased demands for urban water
supplies.
After the 1994-2003 drought, efforts were made to better align water demand and supply
in the southeastern Rio Grande basin; these efforts included buyback of water rights and
infrastructure improvements (e.g., reducing water losses from agricultural and municipal
water distribution systems). Much of the focus has been on reducing agricultural water
use since it accounts for 84% of water withdrawals in the southeastern Rio Grande basin.
Some of these efforts were undertaken binationally.55 Support for some of these
investments was provided by Minute 309.56 Although progress has been made, demand
still exceeds supply.57 Some stakeholders have also questioned how much water savings
has been accomplished through these investments and whether the investments in Mexico
resulted in improved water deliveries by Mexico under the 1944 Water Treaty.58
Responses to Mexico’s Rio Grande Water
Delivery Shortfalls
Stakeholder Perspectives
Some U.S. interests contend that Mexico’s water delivery process treats U.S. deliveries as a
secondary priority to meeting Mexico’s own water uses; this has angered some because of the
more prescriptive nature of the U.S. water delivery requirement to Mexico (i.e., specified
quantities are required to be delivered annually). They point to high storage levels in some
Mexican reservoirs as evidence to support their position. They seek the release of waters from
these reservoirs to help with the agricultural water needs in the most eastern portion of the basin.
These interests see these high reservoir levels as the hoarding of a shared resource.
Other basin stakeholders argue that Mexico’s delivery flexibility was explicitly provided in the
Treaty to deal with the annual variability of water conditions in the basin. While the flexibility in
delivery schedule can be viewed as generous to Mexico, some Mexican interests view the water
delivery requirements in the 1944 Water Treaty as generous to the United States. They argue that
although 30% of the water in the southeastern Rio Grande basin historically originated in the
55 For example, efforts to improve irrigation efficiency in the largest irrigation district in the Rio Conchos basin were
undertaken using assistance from the North American Development Bank (NADBank). NADBank also invested in
irrigation efficiency conveyance improvements in U.S. border counties. NADBank provided $40 million in grants for
these activities in Mexico, and $40 million for activities in the United States (Reed 2007).
56 Minute 309, Volumes of Water Saved with the Modernization and Improved Technology Projects for the Irrigation
Districts in the Rio Conchos Basin and Measures for Their Conveyance to the Rio Grande, July 3, 2003, available at
http://www.ibwc.gov/Files/Minutes/Min309.pdf.
57 Sandoval-Solis 2011.
58 Reed 2007.
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United States, 50% of the basin’s water has been allotted to the United States.59 This occurs in
part because U.S. tributaries are allotted 100% to the United States.
For Mexico, conserving water in its reservoirs can be viewed as part of a long-term drought risk
management strategy. The strategy in some Mexican sub-basins to conserve water in some
reservoirs during drought also may be influenced by the less developed levels of agricultural
insurance and government assistance programs in Mexico. These types of programs in the United
States reduce the agriculture sector’s economic exposure to droughts and other natural disasters.
Some U.S. stakeholders support reevaluating the current binational water-sharing framework for
multiple reasons, including Mexico’s Rio Grande water deliveries, its reservoir management and
plans, and other disputes and concerns (e.g., environmental restoration and protected and invasive
species management issues) in both the Rio Grande and Colorado River basins. Others support
continuing to work within the existing Minute and IBWC framework, including some U.S.
interests that are encouraged by the resolution and cooperation on binational Colorado River
issues and concerned that opening up the 1944 Water Treaty is risky for U.S. interests.
Diplomatic Responses
The IBWC has resolved most border water disputes since 1944, although its processes may be
slow to reach resolution. The IBWC employs a combination of technical expertise and diplomacy
(backed by the State Department and Mexico’s Foreign Ministry) to find solutions that are
acceptable to stakeholders on both sides of the border. As with past crises, the IBWC has been the
primary entity engaged in resolving the current Rio Grande water dispute over how to address dry
conditions and water deliveries in that region.
The U.S. and Mexican Sections of the IBWC have been meeting regularly since late 2012 to
discuss Mexico’s water deliveries. As of early April 2013, the U.S. Section of the IBWC
(USIBWC) reported that the Mexican government had initiated some releases from a reservoir on
the San Rodrigo River per the USIBWC’s (and the Mexican state of Tamaulipas’s)60 repeated
requests.61 Since April 2013, U.S. and Mexican political officials have stepped in to support
IBWC efforts to resolve the current water dispute.
According to U.S. and Mexican officials, the water dispute has been a topic of conversation
between high-level government officials, including during President Obama’s trip to Mexico.62
Mexican officials indicate they understand that the United States does not want to wait for the end
of this five-year delivery period to receive its allotment of Rio Grande water. The
U.S. ambassador to Mexico raised the issue with high-level officials in the administration of
Mexican president Enrique Peña Nieto. President Peña Nieto reportedly does not want this
59 Spener 2013.
60 Spener, 2013.
61 Letter from Edward Drusina, U.S. IBWC Commissioner, to the Honorable U.S. Representatives Cuellar, Gallego,
Hinojosa, and Vela, April 5, 2013.
62 CRS phone interview with State Department official, July 11, 2013; CRS phone interview with Mexican official,
July 5, 2013. Water issues were not included in the joint presidential statement after that meeting nor mentioned in the
remarks made by Presidents Obama and Peña Nieto (The White House, Office of the Press Secretary, “Joint Statement
Between the United States and Mexico,” May 2, 2013; “Remarks by President Obama and President Pena Nieto of
Mexico in a Joint Press Conference,” May 2, 2013).
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dispute to become a serious irritant in the bilateral relationship and has instructed his Foreign
Ministry to prioritize working with the IBWC, the State Department, Mexico’s Water
Commission, and authorities from Texas to reach a mediated settlement to the dispute as soon as
possible.63
Among the outcomes of diplomatic efforts has been an exchange of technical data to assist in
developing options for future water management in the basin. In addition, Mexico delivered more
than the 350,000 AF during the third year of the cycle. According to the IBWC Commissioner,
“This is a consequence to be sure, of beneficial summer precipitation but also is a direct result of
our negotiations achieving a substantially more cooperative approach by Mexican authorities in
reservoir management.”64
Congressional Responses
Several Members of Congress noted the complaints of farmers, local officials, and state officials
about the rate of Mexico’s water deliveries.65 Some Members of Congress have expressed
concerns about the adequacy of USIBWC and State Department efforts to press Mexico to
comply more consistently with its 1944 Water Treaty obligations.
On December 16, 2014, P.L. 113-235, the Consolidated and Further Continuing Appropriations
Act of 2015, became law; Section 7045(g)(3) of Division J of the law required the U.S. Section of
the IBWC to report to the Committees on Appropriations on various water delivery and
accounting issues:
Not later than 45 days after the enactment of this Act, the Secretary of State, in consultation
with the Commissioner for the United States Section of the International Boundary and
Water Commission (IBWC), shall report to the Committees on Appropriations on the efforts
to work with the Mexico Section of the IBWC and the Government of Mexico to establish
mechanisms to improve the transparency of data on, and predictability of, the water
deliveries from Mexico to the United States to meet annual water apportionments to the Rio
Grande, in accordance with the 1944 Treaty between the United States and Mexico
Respecting Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio Grande,
and on actions taken to minimize or eliminate the water deficits owed to the United States in
the current 5-year cycle by the end of such cycle: Provided, That such report shall include a
projection of the balance of the water delivery deficit at the end of the current 5-year cycle,
as well as the estimated impact to the United States of a negative delivery balance.
63 CRS phone interview with State Department official, July 11, 2013; CRS phone interview with Mexican official,
July 5, 2013.
64 Letter from Edward Drusina, IBWC Commissioner, to various Senators and Representatives, October 23, 2013.
65 See, for example, “Water Fights Flare,” Frontera Norte-Sur, May 7, 2013.
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Author Contact Information
Nicole T. Carter
Daniel T. Shedd
Specialist in Natural Resources Policy
Legislative Attorney
ncarter@crs.loc.gov, 7-0854
dshedd@crs.loc.gov, 7-8441
Clare Ribando Seelke
Specialist in Latin American Affairs
cseelke@crs.loc.gov, 7-5229
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