Updated August 23, 2018
Freshwater Harmful Algal Blooms: An Overview
Scientific research indicates that in recent years, the
animal feeding operations (from manure discharge).
frequency and geographic distribution of harmful algal
Nonpoint sources include other animal feeding operations,
blooms (HABs) have been increasing nationally and
agricultural runoff (fertilizers and manure), urban
globally. They have been recorded in all 50 states. HABs
stormwater runoff (fertilizers, pet waste, phosphate-
can be detrimental to human health, pets, livestock, aquatic
containing soaps), failing septic systems, and atmospheric
ecosystems, and the economy.
deposition of nitrogen oxides generated by the combustion
of fossil fuels.
What Are Harmful Algal Blooms?
Algal communities are naturally occurring components of
Efforts to Address Harmful Algal Blooms
healthy aquatic ecosystems, such as lakes, rivers, and
Congress has recognized the increasing frequency of HABs
estuaries. However, under certain environmental
and has passed legislation in an effort to address their
conditions—such as increased temperatures and nutrient
public health, economic, and environmental consequences.
concentrations (e.g., nitrogen and phosphorus)—colonies of
The Harmful Algal Bloom and Hypoxia Research and
algae can grow excessively (or “bloom”) and produce
Control Act of 1998 (HABHRCA) as amended, established
toxins. These HABs sometimes produce discolorations in
an interagency task force, required the task force to prepare
the water that can appear as scums, paint-like slicks, clotted
reports and plans addressing marine and freshwater HABs,
mats, or foam. Even when visible signs of a bloom are
and authorized funding for research, education, monitoring
absent, however, algal toxins may still be harmful.
activities, etc. In 2015, in response to public safety concerns
arising from a major HAB event in Toledo, Ohio, Congress
While many types of algae can cause HABs in bodies of
passed legislation addressing algal toxins in drinking water
freshwater, cyanobacteria typically cause the most frequent
(P.L. 114-45; for more information, see CRS In Focus
and severe blooms. Some species of cyanobacteria produce
IF10269, Algal Toxins in Drinking Water: EPA Health
toxins, called cyanotoxins, which can cause hepatic (liver-
Advisories, by Mary Tiemann). In the Water Infrastructure
related), neurologic, respiratory, dermatologic, and other
Improvements for the Nation Act, P.L. 114-322, Congress
symptoms. These may be acute or chronic, mild or severe,
directed Environmental Protection Agency (EPA) to
and may be fatal in some cases. Humans may be exposed to
designate a Harmful Algal Bloom Coordinator to
cyanotoxins by consuming tainted drinking water, fish, or
coordinate projects and activities involving HABs in the
shellfish; swimming or recreating in waters with certain
Great Lakes. In addition to HAB-specific legislation, the
concentrations of cyanotoxins present; or inhaling
Clean Water Act (CWA, 33 U.S.C. §1251 et seq.)
aerosolized toxins. The cyanotoxins associated with these
authorizes EPA to address water quality concerns
HABs can also kill pets, farm animals, and wildlife, and
associated with HABs.
contaminate or kill fish, leading to recreational, economic,
and environmental losses.
Many federal agencies are involved in carrying out various
HAB-related activities, including conducting HAB
HABs can also contribute to deteriorating water quality and
research, monitoring algal toxins and water quality,
ecosystem health. An over-abundance of cyanobacteria or
forecasting HABs, supporting projects to improve water
other algae can block out sunlight and clog fish gills. In
quality, and community outreach efforts. The federal
addition, as the algae die and decompose, they consume
agencies and organizations specifically required in
oxygen, leaving waterways in a hypoxic (low oxygen) state,
HABHRCA to participate on the interagency task force
sometimes forming dead zones—areas with little or no
include the Department of Commerce, the National Oceanic
oxygen where life cannot survive. Such areas can suffocate
and Atmospheric Administration (NOAA), EPA, the
and kill fish and other aquatic life.
Department of Agriculture, the Department of Interior, the
Department of the Navy, the Department of Health and
What Causes Harmful Algal Blooms?
Human Services, the National Science Foundation, the
Many factors may influence the occurrence and prevalence
National Aeronautics and Space Administration, the Food
of HABs in freshwater, including nutrient concentrations,
and Drug Administration, the Office of Science and
water temperature, availability of light, pH, and water
Technology Policy, the Council on Environmental Quality,
circulation. Nutrient enrichment is widely recognized as
and the Centers for Disease Control and Prevention.
one of the key causes of HAB formation.
After amendments to HABHRCA in 2014 (P.L. 113-124),
While some sources of nutrients in water bodies are natural,
the task force was reconstituted as the Interagency Working
many anthropogenic (i.e., human) activities contribute
Group on the Harmful Algal Bloom and Hypoxia Research
nutrients to waterbodies from a number of point (direct) and
and Control Act, which is responsible for maintaining a
nonpoint (diffuse) sources. Point sources include municipal
national HAB/hypoxia program. NOAA and EPA share
and industrial wastewater discharges and concentrated
primary responsibility under HABHRCA for administering
https://crsreports.congress.gov
Freshwater Harmful Algal Blooms: An Overview
the national HAB and hypoxia program, with NOAA
significantly reduce or eliminate funding for most of these
leading marine aspects of the program and EPA in charge
programs. (For information on financial assistance for
of freshwater aspects. In addition to agencies listed above,
agricultural nutrient management from the U.S. Department
the U.S. Army Corps of Engineers is an active member in
of Agriculture, see CRS Report R43919, Nutrients in
the interagency working group.
Agricultural Production: A Water Quality Overview, by
Megan Stubbs.)
In its role under HABHRCA and the CWA, EPA’s efforts
to address HABs include coordinating the efforts of
Research Gaps
multiple entities, developing regulations and guidelines to
Scientists widely recognize research gaps that hinder the
protect water quality, conducting research, providing
ability to prevent, predict, minimize, and suppress HABs. In
financial assistance through grants and other agreements,
reauthorizing HABHRCA in 2014, Congress directed
and educating the public.
NOAA—through the interagency working group—to
prepare a comprehensive research plan and action strategy
In December 2016, EPA used its authority under the CWA
to address marine and freshwater HABs and hypoxia. A
to propose water quality criteria for two algal toxins in
February 2016 task force report discusses the key
waters used for recreational purposes (81 Federal Register
challenges in HAB and hypoxia management and the gaps
91929). States use such criteria when developing water
in the research and management communities’ knowledge
quality standards—measures that describe the desired
of HAB and hypoxia events. Examples of gaps include the
condition or level of protection of a water body and what is
limited ability to predict the timing, species composition,
needed for protection. Many entities—including states,
and toxicity of HABs and the need to strengthen and
representatives of publicly owned treatment works,
integrate new and existing monitoring programs.
agricultural organizations, and environmental groups—
provided comments on the draft criteria. Some commenters
Issues for Congress
were supportive of the criteria for purposes of informing
While Congress, federal agencies, and states are taking
swimming advisory decisions but did not support the use of
steps to address HABs, many observers assert that further
the criteria for developing water quality standards. They
action is needed to make progress that outpaces the growing
noted, among several implementation concerns, that
consequences of nutrient pollution.
cyanotoxins are not a pollutant discharged into waterways
but rather result from other pollutants (nutrients) entering
Congress has passed legislation to help drive and fund
waterways, among other factors. Some commenters
research efforts and improve collaboration among the
generally supported EPA’s criteria for use in both
many federal agencies involved in HAB-related
swimming advisories and development of water quality
activities. Moving forward, Congress may be interested
standards but also discussed the importance of reducing
in oversight of the Trump Administration’s efforts to
nutrient inputs to address HABs. Regarding the proposed
implement HABHRCA and related authorities.
concentration levels, some commenters felt that they were
overly protective, while others felt they should be more
Most observers agree that further research is needed to
stringent.
understand the most appropriate way to predict,
minimize, and suppress HAB outbreaks, including
EPA has emphasized the need to reduce nutrient pollution
whether and how to regulate algal toxins. These
from all sources to address public health and environmental
advocates assert that Congress should ensure that
impacts associated with HABs. However, the CWA does
adequate funding is available for such research.
not authorize EPA to regulate all sources. It authorizes EPA
to regulate point sources of nutrients but not nonpoint
To control HABs, some advocate regulating nonpoint
sources of nutrient pollution.
source pollution, arguing that point sources are
disproportionately regulated and that nonpoint sources
Some states have developed guidelines for algal toxins,
are the larger contributors to nutrient pollution. Others
primarily for use in guiding swimming advisories. Also,
argue that EPA and other federal agencies should
states have listed waters as impaired, or not meeting water
continue to focus on collaborative, voluntary efforts to
quality standards, for algal blooms or algal toxins. Some of
address nonpoint source pollution that contributes to
these states have begun to develop Total Maximum Daily
HAB formation and that Congress should continue to
Loads (TMDLs)—essentially pollution budgets—to address
fund these programs.
them. Most states have identified nutrient-related pollution
as a priority to be addressed by their TMDLs and/or
For a discussion of the HAB-related bills introduced to date
alternative restoration plans. States rely heavily on financial
in the 115th Congress, as well as further information about
assistance from EPA in implementing these plans and, more
the issues discussed above, see CRS Report R44871,
broadly, in addressing nonpoint source pollution that leads
Freshwater Harmful Algal Blooms: Causes, Challenges,
to degraded water quality and HAB formation. Congress
and Policy Considerations, by Laura Gatz.
has long provided financial assistance through EPA for
regional, state, and local programs through CWA section
Laura Gatz, Analyst in Environmental Policy
106 and 319 planning grants, geographic programs (e.g.,
Chesapeake Bay and Great Lakes), and other sources.
IF10690
President Trump’s FY2019 budget request proposes to
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Freshwater Harmful Algal Blooms: An Overview
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
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