Freshwater Harmful Algal Blooms: An Overview
Updated July 8, 2020
Freshwater Harmful Algal Blooms: An Overview
Scientific research indicates that in recent years, the
operations (from manure discharge). Nonpoint sources
frequency and geographic distribution of harmful algal
include other animal feeding operations, agricultural runoff
blooms (HABs) have been increasing nationally and
(fertilizers and manure), urban stormwater runoff
globally. They have been recorded in all 50 states. HABs
(fertilizers, pet waste, phosphate-containing soaps), failing
can be detrimental to human health, pets, livestock, aquatic
septic systems, and atmospheric deposition of nitrogen
ecosystems, and the economy.
oxides generated by fossil fuel combustion.
What Are Harmful Algal Blooms?
Efforts to Address Harmful Algal Blooms
Algal communities are naturally occurring components of
Congress has recognized the increasing frequency of HABs
healthy aquatic ecosystems, such as lakes, rivers, and
and has passed legislation in an effort to address their
estuaries. However, under certain environmental
public health, economic, and environmental consequences.
conditions—such as increased temperatures and nutrient
The Harmful Algal Bloom and Hypoxia Research and
concentrations (e.g., nitrogen and phosphorus)—colonies of
Control Act of 1998 (HABHRCA) as amended, established
algae can grow excessively (or “bloom”) and produce
an interagency task force, required the task force to prepare
toxins. These HABs sometimes produce discolorations in
reports and plans addressing marine and freshwater HABs,
the water that can appear as scums, paint-like slicks, clotted
and authorized funding for research, education, monitoring
mats, or foam. Even when visible signs of a bloom are
activities, etc. Congress most recently reauthorized
absent, however, algal toxins may still be harmful.
HABHRCA in January 2019 (P.L. 115-423), requiring the
task force to submit a scientific assessment of HABs once
While many types of algae can cause HABs in bodies of
every five years, requiring the National Oceanic and
freshwater, cyanobacteria typically cause the most frequent
Atmospheric Administration (NOAA) to develop and
and severe blooms. Some species of cyanobacteria produce
maintain a public website on HAB and Hypoxia Program
toxins, called cyanotoxins, which can cause hepatic (liver-
activities, and authorizing NOAA or the Environmental
related), neurologic, respiratory, dermatologic, and other
Protection Agency (EPA) to determine that a hypoxia or
symptoms. These may be acute or chronic, mild or severe,
HAB event is an event of national significance.
and may be fatal in some cases. Humans may be exposed to
cyanotoxins by consuming tainted drinking water, fish, or
In 2015, in response to public safety concerns arising from
shellfish; swimming or recreating in waters with certain
a major HAB event in Toledo, Ohio, Congress passed
concentrations of cyanotoxins present; or inhaling
legislation addressing algal toxins in drinking water (P.L.
aerosolized toxins. The cyanotoxins associated with these
114-45; for more information, see CRS In Focus IF10269,
HABs can also kill pets, farm animals, and wildlife, and
Algal Toxins in Drinking Water: EPA Health Advisories).
contaminate or kill fish, leading to recreational, economic,
In the Water Infrastructure Improvements for the Nation
and environmental losses.
Act, Congress directed EPA to designate a Harmful Algal
Bloom Coordinator to coordinate projects and activities
HABs can also contribute to deteriorating water quality and
involving HABs in the Great Lakes. In addition to HAB-
ecosystem health. An over-abundance of cyanobacteria or
specific legislation, the Clean Water Act (CWA) authorizes
other algae can block out sunlight and clog fish gills. In
EPA to address water quality concerns associated with
addition, as the algae die and decompose, they consume
HABs.
oxygen, leaving waterways in a hypoxic (low oxygen) state,
sometimes forming dead zones—areas with little or no
Many federal agencies are involved in carrying out various
oxygen where life cannot survive. Such areas can suffocate
HAB-related activities, including conducting research,
and kill fish and other aquatic life.
monitoring algal toxins and water quality, forecasting
HABs, supporting projects to improve water quality, and
What Causes Harmful Algal Blooms?
facilitating community outreach efforts. The federal
Many factors may influence the occurrence and prevalence
agencies and organizations HABHRCA specifically
of HABs in freshwater, including nutrient concentrations,
requires to participate on the task force include the
water temperature, availability of light, pH, and water
Department of Commerce, NOAA, EPA, Department of
circulation. Nutrient enrichment is widely recognized as
Agriculture, Department of Interior, Department of the
one of the key causes of HAB formation.
Navy, Department of Health and Human Services, National
Science Foundation, National Aeronautics and Space
While some sources of nutrients in waterbodies are natural,
Administration, Food and Drug Administration, Office of
many anthropogenic (i.e., human) activities contribute
Science and Technology Policy, Council on Environmental
nutrients from both point (direct) and nonpoint (diffuse)
Quality, Centers for Disease Control and Prevention, and
sources. Point sources include municipal and industrial
Army Corps of Engineers.
wastewater discharges and concentrated animal feeding
https://crsreports.congress.gov
Freshwater Harmful Algal Blooms: An Overview
After amendments to HABHRCA in 2014, the task force
broadly, in addressing nonpoint source pollution that leads
was reconstituted as the Interagency Working Group on the
to degraded water quality and HAB formation. Congress
Harmful Algal Bloom and Hypoxia Research and Control
has long provided financial assistance through EPA for
Act, which is responsible for maintaining a national
regional, state, and local programs through CWA section
HAB/hypoxia program. NOAA and EPA share primary
106 and 319 planning grants, geographic programs (e.g.,
responsibility for administering the national HAB and
Chesapeake Bay and Great Lakes), and other sources.
hypoxia program, with NOAA leading marine aspects of
President Trump’s FY2021 budget request proposes to
the program and EPA in charge of freshwater aspects.
significantly reduce or eliminate funding for most of these
programs. (For information on financial assistance for
In its role under HABHRCA and the CWA, EPA’s efforts
agricultural nutrient management from the U.S. Department
to address HABs include coordinating efforts of multiple
of Agriculture, see CRS Report R43919, Nutrients in
entities, developing regulations and guidelines to protect
Agricultural Production: A Water Quality Overview.)
water quality, conducting research, providing financial
assistance, and educating the public.
Research Gaps
Scientists widely recognize research gaps that hinder the
In June 2019, EPA used its authority under the CWA to
ability to prevent, predict, minimize, and suppress HABs. In
publish final water quality criteria for two algal toxins in
reauthorizing HABHRCA in 2014, Congress directed
waters used for recreational purposes (84 Federal Register
NOAA—through the interagency working group—to
26413). States may consider such criteria when developing
prepare a comprehensive research plan and action strategy
water quality standards—measures that describe the desired
to address marine and freshwater HABs and hypoxia. A
condition or level of protection of a water body and what is
February 2016 task force report discusses the key
needed for protection. Alternatively, they may use these
challenges in HAB and hypoxia management and the gaps
values as the basis of swimming advisories for public
in the research and management communities’ knowledge
notification purposes at recreational waters. EPA had
of HAB and hypoxia events. Examples of gaps include the
proposed draft criteria in December 2016. Many entities—
limited ability to predict the timing, species composition,
including states, representatives of publicly owned
and toxicity of HABs and the need to strengthen and
treatment works, agricultural organizations, and
integrate new and existing monitoring programs.
environmental groups—provided comments on the draft
criteria. Some were supportive of the criteria for purposes
Issues for Congress
of informing swimming advisory decisions but did not
While Congress, federal agencies, and states are taking
support the use of the criteria for developing water quality
steps to address HABs, many observers assert that further
standards. They noted, among several implementation
action is needed to make progress that outpaces the growing
concerns, that cyanotoxins are not a pollutant discharged
consequences of nutrient pollution.
into waterways but rather result from other pollutants
(nutrients) entering waterways, among other factors. Some
Congress has passed legislation to help drive and fund
commenters generally supported EPA’s criteria for use in
research efforts and improve collaboration among the many
both swimming advisories and development of water
federal agencies involved in HAB-related activities.
quality standards but also discussed the importance of
Moving forward, Congress may be interested in oversight
reducing nutrient inputs to address HABs. Regarding the
of the implementation of HABHRCA and related
proposed concentration levels, some commenters felt that
authorities.
they were overly protective, while others felt they should be
more stringent. EPA’s final recommended concentrations
Most observers agree that further research is needed to
for the two algal toxins are 8 µg/L for microcystin and 15
understand the most appropriate way to predict, minimize,
µg/L for cylindrospermopsin (higher than the draft
and suppress HAB outbreaks, including whether and how to
concentrations of 4 µg/L and 8 µg/L, respectively).
regulate algal toxins. These advocates assert that Congress
should ensure that adequate funding is available for such
EPA has emphasized the need to reduce nutrient pollution
research.
from all sources to address public health and environmental
impacts associated with HABs. However, the CWA does
To control HABs, some advocate regulating nonpoint
not authorize EPA to regulate all sources. It authorizes EPA
source pollution, arguing that point sources are
to regulate point sources of nutrients but not nonpoint
disproportionately regulated while nonpoint sources are the
sources of nutrient pollution.
larger contributors to nutrient pollution. Others argue that
EPA and other federal agencies should continue to focus on
Some states have developed guidelines for algal toxins,
collaborative, voluntary efforts to address nonpoint source
primarily for use in guiding swimming advisories. Also,
pollution that contributes to HAB formation and that
states have listed waters as impaired, or not meeting water
Congress should continue to fund these programs.
quality standards, for algal blooms or algal toxins. Some of
For a discussion of the HAB-related bills introduced to date
these states have begun to develop Total Maximum Daily
in the 116th Congress, as well as further information about
Loads (TMDLs)—essentially pollution budgets—to address
the issues discussed above, see CRS Report R44871,
them. Most states have identified nutrient-related pollution
Freshwater Harmful Algal Blooms: Causes, Challenges,
as a priority to be addressed by their TMDLs and/or
and Policy Considerations.
alternative restoration plans. States rely heavily on financial
assistance from EPA in implementing these plans and, more
Laura Gatz, Analyst in Environmental Policy
https://crsreports.congress.gov
Freshwater Harmful Algal Blooms: An Overview
IF10690
Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff to
congressional committees and Members of Congress. It operates solely at the behest of and under the direction of Congress.
Information in a CRS Report should not be relied upon for purposes other than public understanding of information that has
been provided by CRS to Members of Congress in connection with CRS’s institutional role. CRS Reports, as a work of the
United States Government, are not subject to copyright protection in the United States. Any CRS Report may be
reproduced and distributed in its entirety without permission from CRS. However, as a CRS Report may include
copyrighted images or material from a third party, you may need to obtain the permission of the copyright holder if you
wish to copy or otherwise use copyrighted material.
https://crsreports.congress.gov | IF10690 · VERSION 6 · UPDATED