Freshwater Harmful Algal Blooms: An Overview

Updated July 8, 2020

Freshwater Harmful Algal Blooms: An Overview

Scientific research indicates that in recent years, the

frequency and geographic distribution of harmful algal

blooms (HABs) have been increasing nationally and

globally. They have been recorded in all 50 states. HABs

can be detrimental to human health, pets, livestock, aquatic

ecosystems, and the economy.

operations (from manure discharge). Nonpoint sources

include other animal feeding operations, agricultural runoff

(fertilizers and manure), urban stormwater runoff

(fertilizers, pet waste, phosphate-containing soaps), failing

septic systems, and atmospheric deposition of nitrogen

oxides generated by fossil fuel combustion.

What Are Harmful Algal Blooms?

Efforts to Address Harmful Algal Blooms

Algal communities are naturally occurring components of

healthy aquatic ecosystems, such as lakes, rivers, and

estuaries. However, under certain environmental

conditions—such as increased temperatures and nutrient

concentrations (e.g., nitrogen and phosphorus)—colonies of

algae can grow excessively (or “bloom”) and produce

toxins. These HABs sometimes produce discolorations in

the water that can appear as scums, paint-like slicks, clotted

mats, or foam. Even when visible signs of a bloom are

absent, however, algal toxins may still be harmful.

Congress has recognized the increasing frequency of HABs

and has passed legislation in an effort to address their

public health, economic, and environmental consequences.

The Harmful Algal Bloom and Hypoxia Research and

Control Act of 1998 (HABHRCA) as amended, established

an interagency task force, required the task force to prepare

reports and plans addressing marine and freshwater HABs,

and authorized funding for research, education, monitoring

activities, etc. Congress most recently reauthorized

HABHRCA in January 2019 (P.L. 115-423), requiring the

task force to submit a scientific assessment of HABs once

every five years, requiring the National Oceanic and

Atmospheric Administration (NOAA) to develop and

maintain a public website on HAB and Hypoxia Program

activities, and authorizing NOAA or the Environmental

Protection Agency (EPA) to determine that a hypoxia or

HAB event is an event of national significance.

While many types of algae can cause HABs in bodies of

freshwater, cyanobacteria typically cause the most frequent

and severe blooms. Some species of cyanobacteria produce

toxins, called cyanotoxins, which can cause hepatic (liverrelated), neurologic, respiratory, dermatologic, and other

symptoms. These may be acute or chronic, mild or severe,

and may be fatal in some cases. Humans may be exposed to

cyanotoxins by consuming tainted drinking water, fish, or

shellfish; swimming or recreating in waters with certain

concentrations of cyanotoxins present; or inhaling

aerosolized toxins. The cyanotoxins associated with these

HABs can also kill pets, farm animals, and wildlife, and

contaminate or kill fish, leading to recreational, economic,

and environmental losses.

HABs can also contribute to deteriorating water quality and

ecosystem health. An over-abundance of cyanobacteria or

other algae can block out sunlight and clog fish gills. In

addition, as the algae die and decompose, they consume

oxygen, leaving waterways in a hypoxic (low oxygen) state,

sometimes forming dead zones—areas with little or no

oxygen where life cannot survive. Such areas can suffocate

and kill fish and other aquatic life.

What Causes Harmful Algal Blooms?

Many factors may influence the occurrence and prevalence

of HABs in freshwater, including nutrient concentrations,

water temperature, availability of light, pH, and water

circulation. Nutrient enrichment is widely recognized as

one of the key causes of HAB formation.

While some sources of nutrients in waterbodies are natural,

many anthropogenic (i.e., human) activities contribute

nutrients from both point (direct) and nonpoint (diffuse)

sources. Point sources include municipal and industrial

wastewater discharges and concentrated animal feeding

In 2015, in response to public safety concerns arising from

a major HAB event in Toledo, Ohio, Congress passed

legislation addressing algal toxins in drinking water (P.L.

114-45; for more information, see CRS In Focus IF10269,

Algal Toxins in Drinking Water: EPA Health Advisories).

In the Water Infrastructure Improvements for the Nation

Act, Congress directed EPA to designate a Harmful Algal

Bloom Coordinator to coordinate projects and activities

involving HABs in the Great Lakes. In addition to HABspecific legislation, the Clean Water Act (CWA) authorizes

EPA to address water quality concerns associated with

HABs.

Many federal agencies are involved in carrying out various

HAB-related activities, including conducting research,

monitoring algal toxins and water quality, forecasting

HABs, supporting projects to improve water quality, and

facilitating community outreach efforts. The federal

agencies and organizations HABHRCA specifically

requires to participate on the task force include the

Department of Commerce, NOAA, EPA, Department of

Agriculture, Department of Interior, Department of the

Navy, Department of Health and Human Services, National

Science Foundation, National Aeronautics and Space

Administration, Food and Drug Administration, Office of

Science and Technology Policy, Council on Environmental

Quality, Centers for Disease Control and Prevention, and

Army Corps of Engineers.

https://crsreports.congress.gov

Freshwater Harmful Algal Blooms: An Overview

After amendments to HABHRCA in 2014, the task force

was reconstituted as the Interagency Working Group on the

Harmful Algal Bloom and Hypoxia Research and Control

Act, which is responsible for maintaining a national

HAB/hypoxia program. NOAA and EPA share primary

responsibility for administering the national HAB and

hypoxia program, with NOAA leading marine aspects of

the program and EPA in charge of freshwater aspects.

In its role under HABHRCA and the CWA, EPA’s efforts

to address HABs include coordinating efforts of multiple

entities, developing regulations and guidelines to protect

water quality, conducting research, providing financial

assistance, and educating the public.

In June 2019, EPA used its authority under the CWA to

publish final water quality criteria for two algal toxins in

waters used for recreational purposes (84 Federal Register

26413). States may consider such criteria when developing

water quality standards—measures that describe the desired

condition or level of protection of a water body and what is

needed for protection. Alternatively, they may use these

values as the basis of swimming advisories for public

notification purposes at recreational waters. EPA had

proposed draft criteria in December 2016. Many entities—

including states, representatives of publicly owned

treatment works, agricultural organizations, and

environmental groups—provided comments on the draft

criteria. Some were supportive of the criteria for purposes

of informing swimming advisory decisions but did not

support the use of the criteria for developing water quality

standards. They noted, among several implementation

concerns, that cyanotoxins are not a pollutant discharged

into waterways but rather result from other pollutants

(nutrients) entering waterways, among other factors. Some

commenters generally supported EPA’s criteria for use in

both swimming advisories and development of water

quality standards but also discussed the importance of

reducing nutrient inputs to address HABs. Regarding the

proposed concentration levels, some commenters felt that

they were overly protective, while others felt they should be

more stringent. EPA’s final recommended concentrations

for the two algal toxins are 8 µg/L for microcystin and 15

µg/L for cylindrospermopsin (higher than the draft

concentrations of 4 µg/L and 8 µg/L, respectively).

EPA has emphasized the need to reduce nutrient pollution

from all sources to address public health and environmental

impacts associated with HABs. However, the CWA does

not authorize EPA to regulate all sources. It authorizes EPA

to regulate point sources of nutrients but not nonpoint

sources of nutrient pollution.

Some states have developed guidelines for algal toxins,

primarily for use in guiding swimming advisories. Also,

states have listed waters as impaired, or not meeting water

quality standards, for algal blooms or algal toxins. Some of

these states have begun to develop Total Maximum Daily

Loads (TMDLs)—essentially pollution budgets—to address

them. Most states have identified nutrient-related pollution

as a priority to be addressed by their TMDLs and/or

alternative restoration plans. States rely heavily on financial

assistance from EPA in implementing these plans and, more

broadly, in addressing nonpoint source pollution that leads

to degraded water quality and HAB formation. Congress

has long provided financial assistance through EPA for

regional, state, and local programs through CWA section

106 and 319 planning grants, geographic programs (e.g.,

Chesapeake Bay and Great Lakes), and other sources.

President Trump’s FY2021 budget request proposes to

significantly reduce or eliminate funding for most of these

programs. (For information on financial assistance for

agricultural nutrient management from the U.S. Department

of Agriculture, see CRS Report R43919, Nutrients in

Agricultural Production: A Water Quality Overview.)

Research Gaps

Scientists widely recognize research gaps that hinder the

ability to prevent, predict, minimize, and suppress HABs. In

reauthorizing HABHRCA in 2014, Congress directed

NOAA—through the interagency working group—to

prepare a comprehensive research plan and action strategy

to address marine and freshwater HABs and hypoxia. A

February 2016 task force report discusses the key

challenges in HAB and hypoxia management and the gaps

in the research and management communities’ knowledge

of HAB and hypoxia events. Examples of gaps include the

limited ability to predict the timing, species composition,

and toxicity of HABs and the need to strengthen and

integrate new and existing monitoring programs.

Issues for Congress

While Congress, federal agencies, and states are taking

steps to address HABs, many observers assert that further

action is needed to make progress that outpaces the growing

consequences of nutrient pollution.

Congress has passed legislation to help drive and fund

research efforts and improve collaboration among the many

federal agencies involved in HAB-related activities.

Moving forward, Congress may be interested in oversight

of the implementation of HABHRCA and related

authorities.

Most observers agree that further research is needed to

understand the most appropriate way to predict, minimize,

and suppress HAB outbreaks, including whether and how to

regulate algal toxins. These advocates assert that Congress

should ensure that adequate funding is available for such

research.

To control HABs, some advocate regulating nonpoint

source pollution, arguing that point sources are

disproportionately regulated while nonpoint sources are the

larger contributors to nutrient pollution. Others argue that

EPA and other federal agencies should continue to focus on

collaborative, voluntary efforts to address nonpoint source

pollution that contributes to HAB formation and that

Congress should continue to fund these programs.

For a discussion of the HAB-related bills introduced to date

in the 116th Congress, as well as further information about

the issues discussed above, see CRS Report R44871,

Freshwater Harmful Algal Blooms: Causes, Challenges,

and Policy Considerations.

Laura Gatz, Analyst in Environmental Policy

https://crsreports.congress.gov

Freshwater Harmful Algal Blooms: An Overview

IF10690

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