Freshwater Harmful Algal Blooms: Causes, Challenges, and Policy Considerations
Released: 2018-08-20T00:00:00

Summary:
Scientific research indicates that in recent years, the frequency and geographic distribution of harmful algal blooms (HABs) have been increasing nationally and globally. Because the impacts of HABs can be severe and widespread—often with interstate implications—these issues have been a perennial interest for Congress. While algal communities are natural components of healthy aquatic ecosystems, under certain conditions (e.g., increased temperatures and nutrient concentrations), algae may grow excessively, or "bloom," and produce toxins that can harm human health, animals, aquatic ecosystems, and the economy.
In 2014, a cyanobacterial HAB in Lake Erie affected the drinking water for more than 500,000 people in Toledo, Ohio. In 2016, a massive HAB in Florida's Lake Okeechobee negatively impacted tourism and aquatic life. HABs have been recorded in every state and have become a concern nationwide.
Many types of algae can cause HABs in freshwater systems. The most frequent and severe blooms involve the proliferation of cyanobacteria. Some cyanobacteria species can produce toxins—cyanotoxins—that can cause mild to severe health effects in humans and kill aquatic life and other animals.
HABs can also contribute to deteriorating water quality and ecosystem health. As masses of cyanobacteria or other algae die and decompose, they consume oxygen, sometimes forming "dead zones" where life cannot survive. These areas can kill fish and organisms, such as crabs and clams, and have detrimental economic effects.
Scientists widely consider nutrient enrichment to be a key cause of HAB formation. While nutrients are essential to plants and natural parts of aquatic ecosystems, excessive amounts can overstimulate algal growth. Sources include point sources (e.g., municipal wastewater discharges) and nonpoint sources (e.g., fertilizer runoff from agricultural and urban areas).
Congress, federal agencies, and states have taken steps to address HABs and nutrients that contribute to their occurrence. 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.
In December 2016, the Environmental Protection Agency (EPA) used its authority under the Clean Water Act (CWA) to propose water quality criteria for two algal toxins in waters used for recreational purposes. States use 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.
Further, EPA has emphasized the need to reduce nutrient pollution from all sources to reduce public health and environmental impacts associated with HABs. The CWA does not authorize EPA to regulate all sources. It authorizes EPA to regulate point (direct) sources of nutrients but does not authorize EPA to regulate nonpoint (diffuse) 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 Sections 106 and 319 planning grants, geographic programs (such as the Chesapeake Bay and Great Lakes), and other sources. The President's FY2019 budget request for most of these programs is either eliminated or significantly reduced.
Congress continues to show interest in addressing HABs. This interest has largely focused on funding research to close research gaps identified by scientists and decisionmakers and to coordinate the efforts of federal agencies and their partners to study and address HABs.

subsections: section_title: Introduction
paragraphs: Scientific research indicates that in recent years, the frequency and geographic distribution of harmful algal blooms (HABs) have been increasing nationally and globally. HABs can be detrimental to human health, animals, aquatic ecosystems, and local economies. In 2014, a major HAB in Lake Erie caused the city of Toledo, Ohio, to issue a "do not drink" order for tap water that left more than 500,000 people without drinking water for two days and had an estimated impact of $65 million in lost benefits. In the summer of 2016, a massive HAB in Lake Okeechobee—Florida's largest freshwater lake—resulted in beach closures, losses to the tourism industry, and negative impacts on marine life. According to the U.S. Environmental Protection Agency (EPA), between January 1 and August 12, 2016, states reported at least 266 notices for freshwater HABs, including cautions, warnings, public health advisories, and public health warnings.
Congress, many federal agencies, states, localities, and other partners have taken and continue to take steps to address the rising trend in HABs and their impacts. However, there are many gaps in current scientific understanding of HABs among the research and management communities and considerable debate as to how best to address the issue from a regulatory standpoint. This report explores these issues as they pertain to HABs in freshwater systems. Specifically, it addresses the conditions and activities that contribute to the occurrence of freshwater HABs; steps that Congress, federal agencies—particularly EPA—and their partners are taking to address and mitigate their occurrence; and the current knowledge gaps on this issue. This report is focused on freshwater HABs, not marine or coastal HABs or issues associated with HABs in drinking water supplies. 
section_title: Background
subsections: section_title: What Are Harmful Algal Blooms?
paragraphs: 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 that pose a threat to human and aquatic ecosystem health and potentially cause economic damage. These HABs sometimes produce discolorations in the water that can appear as scums, paint-like slicks, clotted mats, or foam that may vary in color (i.e., light to dark green, yellow, red, or brown). Even when visible signs of a bloom are absent, however, algal toxins may still cause harmful effects. Figure 1 shows an aerial view of a HAB that produced visible green scums in Lake Okeechobee, Florida, in July 2016.
subsections: section_title: HAB Types and Impacts
paragraphs: While many types of algae can cause HABs in bodies of freshwater, cyanobacteria (sometimes referred to as blue-green algae) typically cause the most frequent and severe blooms. Cyanobacterial HABs pose a threat to human and aquatic ecosystem health and can kill pets, livestock, and wildlife. Some species of cyanobacteria produce toxins, called cyanotoxins, which can cause hepatic (liver-related), neurologic, respiratory, dermatologic, and other symptoms. These may be acute or chronic, mild or severe, and in some cases may be fatal. 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 contaminate fish, interfere with a variety of recreational activities, and cause other economic and environmental damages.
There are many types of cyanotoxins, which may have multiple variants with a wide range of toxicities. The most commonly occurring and most studied cyanotoxin is microcystin.
Although cyanobacterial HABs are considered to be the most prevalent and toxic types of HABs, blooms of "golden algae" ( Prymnesium parvum ) are an emerging problem and likely the most problematic of non-cyanobacterial freshwater HAB taxa (i.e., group of related organisms classified as a unit). Golden algal HABs have caused large fish kills worldwide, including millions of fish in Texas. Most of the major fish kills have occurred since 2000. Golden algae thrive in brackish water, such as the rivers and reservoirs found in areas of Texas, Oklahoma, and Wyoming. The toxins produced by golden algae target gill-breathing organisms, such as fish, clams, and mussels. According to information from two states that experience golden algal blooms, there is currently no evidence that golden algal toxins pose a direct threat to humans, other mammals, or birds. Effects of cyanobacterial HABs and golden algae HABs are detailed in Table 1 .
In addition to the effects of algal toxins on human and animal health, HABs can also contribute to deteriorating water quality and ecosystem health. An overabundance 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 (or low oxygen) state, sometimes forming "dead zones"—areas where life cannot survive due to lack of oxygen. Low oxygen areas can suffocate and kill fish and bottom-dwelling organisms such as crabs and clams. According to EPA, over 166 dead zones have been documented nationwide, including in waterbodies such as the Chesapeake Bay and the Gulf of Mexico. Significant economic losses have occurred as a result of hypoxia.
section_title: Factors Contributing to HAB Formation
paragraphs: 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. Nutrients, such as nitrogen and phosphorus, are essential to plant growth and natural parts of aquatic ecosystems. However, when high levels of nutrients enter a body of water, they stimulate plant and algal growth, which can lead to depletion of dissolved oxygen (as explained above), reduced transparency (i.e., turbidity), changes to the biological community (e.g., loss of sportfish, such as bass), and degradation of the aesthetic appeal of the water (i.e., from odor and scums). This process is called eutrophication. 
While some sources of nutrients in water bodies are natural, many anthropogenic activities contribute nutrients to waterbodies from a number of point and nonpoint sources. Point sources include municipal and industrial wastewater discharges and concentrated animal feeding operations (CAFOs). Nonpoint sources include urban stormwater runoff, failing septic systems, atmospheric deposition of nitrogen from fossil fuel emissions, runoff from fertilized cropland, and manure runoff from cropland, pastures, and animal feeding operations. See Table 2 for more information on these sources.
Studies also indicate that increased temperatures and changes in frequency and intensity of rainfall associated with climate change may also favor HAB formation. HABs generally proliferate in warmer waters. In addition, some studies have found that swings between flooding and drought may enhance HAB formation. For example, if intense rainfall is followed by a drought, the nutrients washed into receiving water bodies may remain in them longer, increasing the potential for HABs. 
section_title: Incidence and Trends
paragraphs: Scientists largely agree that the frequency and distribution of HABs, the economic losses from them, the types of resources affected, and the number of toxins and toxic species have all increased in recent years. Some scientists note that factors such as better detection methods and increased reporting have contributed to the upward trend. HABs, including cyanobacterial HABs, have been recorded in the waters of all 50 states, with some HABs crossing state lines. Figure 2 shows the generalized distribution of selected freshwater HAB events (cyanobacterial HABs and golden algal HABs) that took place between 2006 and 2015 across the United States. 
The findings of EPA's most recent national assessment of lakes are consistent with other reports of the rising trend in HABs. In EPA's 2012 National Lake Assessment, EPA concluded that there was little change from its 2007 survey of lakes, with two exceptions—trends in algal toxin and nutrient measures. In 2012, EPA and its partners detected microcystin in 39% of lakes, a 9.5% increase from 2007. EPA noted, however, that for both studies, the concentrations of microcystin remained low and rarely exceeded the levels of concern established by the World Health Organization for recreational uses (see " Regulatory Efforts and Guidelines "). EPA also found an 8.3% increase in the percentage of lakes in the "most disturbed condition" category when analyzing the density of cyanobacterial cells (i.e., an indicator of risk for exposure to algal toxins because the cells may produce toxins). Finally, EPA found an overall increase in the median concentration of phosphorus across all lakes and a "dramatic" decline (18.2%) in the percentage of lakes with low nutrients and high oxygen levels. These findings are important because in many lakes, phosphorus is considered the limiting nutrient, meaning that the available quantity of this nutrient controls the pace of algal production. It also means that even small increases in phosphorus can lead to very rapid increases in algal growth. More broadly, the study found that nutrient pollution is a widespread problem across the country. Approximately 35% of lakes have excessive levels of total nitrogen, and 40% of lakes have excessive levels of total phosphorus. 
section_title: Efforts to Address Harmful Algal Blooms
subsections: section_title: Enacted Legislation
paragraphs: Congress has recognized the increasing frequency of HABs and has passed legislation in an effort to address public health, economic, and environmental consequences of HABs. In 1998, Congress passed the Harmful Algal Bloom and Hypoxia Research and Control Act (HABHRCA), which established an Interagency Task Force on Harmful Algal Blooms and Hypoxia. It required the task force to prepare reports assessing HABs and hypoxia with a focus on coastal waters and authorized funding for HAB and hypoxia-related research, education, and monitoring activities. The Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) chaired the task force. In 2004, Congress reauthorized HABHRCA and expanded it to include assessments of HABs in freshwater. In 2014, Congress again reauthorized HABHRCA and established a national HAB/Hypoxia Program to be maintained by NOAA through the task force. It identified NOAA and EPA as the lead federal agencies for marine and freshwater aspects of the program, respectively, and required additional reports and a comprehensive research plan and action strategy. 
In 2015, in response to public safety concerns arising from the Toledo, Ohio, HAB event, Congress passed legislation addressing algal toxins in drinking water. The Drinking Water Protection Act amended the Safe Drinking Water Act to require EPA to develop a strategic plan to assess and manage the risks associated with algal toxins in public drinking water supplies. 
The following year, Congress included a provision in the Water Infrastructure Improvements for the Nation (WIIN) Act that required EPA to designate a Harmful Algal Bloom Coordinator to coordinate projects and activities under the Great Lakes Restoration Initiative involving HABs in the Great Lakes. Table 3 provides a list and description of the HAB-specific legislation enacted since 1998.
In addition to HAB-specific legislation, the Clean Water Act (CWA) authorizes EPA to address water quality concerns associated with HABs. The act establishes a system, under Section 303, for states to adopt ambient water quality standards consisting of the designated use or uses of a water body (e.g., recreational, public water supply, or aquatic life) and the water quality criteria that are necessary to protect the use or uses. States then use their water quality standards to determine which waters must be cleaned up, how much effluent may be discharged, and what is needed for protection. 
Section 304(a) requires the EPA Administrator to publish and, from time to time, revise water quality criteria that accurately reflect the latest scientific knowledge on the kind and extent of all identifiable effects on human health and the environment that might be expected from the presence of pollutants. These criteria constitute guidance that states use in adopting their water quality standards. As recognized by Section 510 of the CWA, states may develop water quality standards that are more stringent than required by EPA regulations. EPA's water quality standards regulations require that in developing water quality standards, states must adopt water quality criteria that protect the designated use. States are to establish numerical criteria —based on (1) EPA's recommended criteria, (2) EPA's criteria modified to reflect site-specific conditions, or (3) other scientifically defensible methods—and establish narrative criteria or criteria based on biomonitoring methods where numerical criteria cannot be established or to supplement numerical criteria.
Section 303(d) of the CWA requires states to identify waters that are impaired by pollution, even after application of pollution controls. For those waters, states must establish a Total Maximum Daily Load (TMDL) of pollutants to ensure that water quality standards can be attained. A TMDL is a quantitative assessment of pollution sources and pollutant reductions needed to restore and protect U.S. waters; it is also a planning process for attaining water quality standards. TMDLs may address all pollution sources, including point sources, such as municipal sewage treatment or industrial plant discharges, and nonpoint sources such as urban runoff and agricultural runoff.
Also, Section 118 of the CWA provides that the United States should seek to attain the goals embodied in the Great Lakes Water Quality Agreement of 1978, as amended by the Water Quality Agreement of 1987 and any other agreements and amendments. It tasks EPA to take the lead in the effort to meet the agreement's goals, working with other federal agencies, states, and localities. As seen in the text box, the most recent amendment includes a HAB-related goal.
section_title: Federal Agency Efforts
paragraphs: Many federal agencies are involved in carrying out various HAB-related activities, including conducting HAB research, monitoring algal toxins and water quality, forecasting HABs, supporting projects to improve water quality, and community outreach efforts. Some in Congress, however, have expressed concern about the activities and expenditures of various agencies and potential redundancies. In the Drinking Water Protection Act ( P.L. 114-45 ), enacted August 7, 2015, Congress directed the Government Accountability Office (GAO) to inventory funds expended by federal agencies to examine toxin-producing cyanobacteria and algae or address public health concerns related to harmful algal blooms. GAO was to recommend ways to improve interagency coordination and reduce duplication of efforts. According to the 2016 GAO report that responded to the mandate, 17 agencies conducted research, monitoring, response, or other HAB-related activities between FY2013 and FY2015. The GAO report provides detailed information on federal agencies' key HAB-related activities, expenditures, and specific statutory authorities, and, thus, this report will not discuss these in detail. Rather, this section identifies the federal agencies involved in a key interagency effort and highlights actions EPA specifically is taking in its role as the leader of freshwater HAB issues.
As previously mentioned, HABHRCA established an interagency task force that is charged with
promoting a national strategy to help communities understand, predict, control, and mitigate freshwater and marine HAB and hypoxia events; enhancing, coordinating, and assessing the activities of existing HABs and hypoxia programs; and providing for development of a comprehensive research plan and action strategy. 
 Table 4 provides a list of the federal agencies and organizations specifically required in HABHRCA to participate on the task force. The reauthorization of HABHRCA in 2014 reconstituted the task force as the Interagency Working Group on the Harmful Algal Bloom and Hypoxia Research and Control Act (IWG-HABHRCA), responsible for maintaining a national HAB/hypoxia program. NOAA and EPA share primary responsibility under HABHRCA for administering the national HAB and hypoxia program, with NOAA leading marine aspects of the program and EPA in charge of freshwater aspects. In addition to agencies listed in the table, the U.S. Army Corps of Engineers is an active member in the IWG-HABHRCA.
In its role under HABHRCA and the CWA, EPA's efforts to address HABs include coordinating the efforts of multiple entities, developing regulations and guidelines to protect water quality (see " Regulatory Efforts and Guidelines " section), conducting research, providing financial assistance through grants and other agreements, and educating the public. In its coordination role, EPA leads, chairs, or cochairs several working groups or task forces, including the IWG-HABHRCA, the Inland HAB Discussion Group, the Great Lakes Interagency Task Force, and the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force (Hypoxia Task Force). See Table 5 for a description of these efforts. 
EPA has also conducted internal research on HABs and their toxins focused on water quality (including how different factors such as nutrients, light, temperature, etc., affect HAB occurrence and toxicity), human and ecological health effects, monitoring and analytical methods research, and drinking water treatment research. The agency also provides research grants, such as those provided through the Science to Achieve Results (STAR) program, focused on topic areas including the prediction, prevention, control, and mitigation of freshwater HABs and the fate and effects from less-common emerging HABs.
EPA also provides financial assistance to states, tribes, and others to address water pollution, including nonpoint source pollution. Examples of such assistance include nonpoint source implementation grants under CWA Section 319, capitalization grants under the Clean Water State Revolving Fund, and grants under CWA Section 106, which are provided to states, interstate agencies, and tribes to administer programs that prevent, reduce, and eliminate water pollution.
section_title: Regulatory Efforts and Guidelines
paragraphs: EPA and states have also taken steps to address HABs and nutrient loads that contribute to their proliferation through regulatory efforts and guidelines. This section focuses on regulatory efforts and guidelines related to EPA's authorities under the CWA and specifically excludes efforts under the Safe Drinking Water Act.
subsections: section_title: HABs, Cyanobacteria, and Cyanotoxins
paragraphs: EPA, the World Health Organization (WHO), and many states have developed guidelines for cyanotoxins in recreational waters. These guidelines are summarized in Table 6 and discussed below.
subsections: section_title: EPA Guidelines
paragraphs: In December 2016, EPA issued draft recreational water quality criteria for microcystins and cylindrospermopsin for public comment. According to EPA, these criteria reflect the concentrations of two cyanotoxins that would be protective of human health in recreational waters used for swimming or other activities: 4 µg/L for microcystin and 8 µg/L for cylindrospermopsin. EPA suggests that states may consider using the proposed values when determining whether to post swimming advisories in recreational waters and may consider using the same values when adopting new or revised water quality standards.
Many entities—including states, representatives of publicly owned treatment works, agricultural organizations, and environmental groups—provided comments on the draft criteria:
Some commenters, including states, 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, noting, among other concerns, that cyanotoxins are not a pollutant discharged into waterways but rather result from other pollutants (nutrients) entering waterways and other factors. Environmental groups generally supported EPA's criteria for use in both swimming advisories and development of water quality standards. Commenters' opinions varied regarding the proposed concentrations of microcystin and cylindrospermopsin in the draft criteria. Some states felt the levels were appropriate, environmental groups felt they should be more stringent, and other states suggested they are overly protective, particularly when compared to the WHO guideline for microcystin. 
Many commenters—particularly states, publicly owned treatment works, and agricultural groups—expressed a number of implementation concerns. One key concern raised was that these criteria, if used for water quality standards, would improperly regulate response organisms rather than a discharged pollutant. Some argued that algal toxins are not a pollutant that CWA permittees discharge. Rather, the discharge of other pollutants, such as excess nutrients, may lead to HAB formation. In its draft criteria document, EPA explained that it does not anticipate states using the criteria alone for permitting purposes, recognizing that cyanobacteria and their toxins are not typically present in permitted discharges. EPA goes on to say the following:
Permits are more likely to be written to address point source discharges of the causal pollutants, such as nutrients, on a waterbody-specific or watershed basis, where the permit writer has determined there is a reasonable potential for the causal pollutants in the discharge to cause or contribute to an exceedance of the cyanotoxin standards.
In this regard, some commenters expressed concern that it is not known precisely what level of nutrients will result in a bloom, nor is it understood what factors will trigger the release of toxins. Several commenters suggested that EPA explore these issues further before moving forward with water quality criteria for purposes other than guiding advisory levels for swimming.
Many commenters also expressed implementation concerns regarding monitoring and sampling. According to the Association of Clean Water Administrators many states do not currently have mechanisms in place to adequately sample for the levels of the toxins specified by EPA or lack adequate lab capacity to process increased samples. Some states, publicly owned treatment works, and agricultural groups also commented that the variability of HABs within a body of water and over even short spans of time can make sampling and analysis complicated, particularly when using the data to determine if a water body is impaired. The commenters urged EPA to address these issues in detail before moving forward with the criteria.
section_title: WHO Guidelines
paragraphs: In 2003, WHO proposed guideline values for protection from adverse health outcomes associated with cyanobacteria blooms in fresh water used for recreational purposes. The guidelines are defined at three levels: low, moderate, and high probability of adverse health effects. WHO concluded that a single guideline value was not appropriate because "it is necessary to differentiate between the chiefly irritative symptoms caused by unknown cyanobacterial substances and the potentially more severe hazard of exposure to high concentrations of known cyanotoxins, particularly microcystins." Table 6 shows the WHO guideline levels for microcystin.
section_title: State Guidelines
paragraphs: According to EPA documents, approximately 30 states have implemented cyanobacterial HAB guidelines for recreational waterways as of November 2015. Some of these states use qualitative guidelines only (i.e., visual inspection for blooms rather than quantitative detection methods) or quantitative guidelines for cyanobacterial cell density rather than guidelines for the specific cyanotoxins. 
Of the 30 states that have implemented cyanobacterial HAB guidelines, 21 have established numeric guidelines for microcystin or cylindrospermopsin. The levels and associated actions vary considerably among states (see Table 6 ). California has adopted the strictest concentrations for both cyanotoxins (0.8 µg/L for microcystin and 4 µg/L for cylindrospermopsin). Several states have adopted the WHO value of 20 µg/L for microcystin. Only seven states have adopted quantitative guidelines for cylindrospermopsin.
Some states have also added waters affected by algal blooms and algal toxins to their impaired water lists (i.e., Section 303(d) lists) for algal blooms and algal toxins. According to data from EPA's Assessment and Total Maximum Daily Load Tracking and Implementation System, 24 states have listed waters impaired for algal blooms, and two states—California and New Hampshire—have listed waters impaired for algal toxins (see Table 7 ). California has listed only one of its waters as impaired for algal toxins and has not yet developed a TMDL. New Hampshire has listed 66 of its waters as impaired for algal toxins and has developed one TMDL that covers two waters. The New Hampshire TMDL establishes a total phosphorus loading target that, if met, is expected to achieve state water quality criteria and thresholds for dissolved oxygen, chlorophyll a (an indicator of algae), and cyanobacteria.
section_title: Nutrient Management
paragraphs: Scientists and policymakers widely recognize the need to reduce nutrient inputs to aquatic systems to limit eutrophication and proliferation of HABs. According to EPA, nitrogen and phosphorus pollution is one of the most serious and pervasive water quality problems in the United States. While EPA and states have worked to address nutrient pollution for over a decade, many observers believe more progress is needed to reduce the threat to water quality and public health. EPA has acknowledged that without greater progress, "the successes to date will likely be outpaced by the rapidly increasing population and the resulting increase in the rate and impact of nitrogen and phosphorus pollution."
According to EPA, 45 states identified nutrient-related pollution as a priority to be addressed by TMDLs and/or alternative restoration plans in setting long-term priorities for their CWA Section 303(d) programs. To date, more than 8,600 nutrient-related TMDLs have been established, primarily by states, to guide nutrient reduction efforts in more than 5,800 waterbodies. 
In 2016, EPA issued a memorandum with a renewed call to states and stakeholders to intensify their efforts, in collaboration with EPA, to reduce nutrient pollution. The memorandum emphasized EPA's support for state planning or implementation of watershed-based, multistakeholder projects to reduce the impacts to public health from nitrogen and phosphorus pollution contributing to HABs. EPA listed and described key elements of its plans for working with partners and stakeholders over the next several years, including prioritizing watersheds and setting load reduction goals, developing numeric nutrient criteria, reducing point sources of nutrient pollution, reducing nutrient loads from nonpoint sources, and providing financial and technical assistance.
For almost two decades, EPA has expressed support for developing numeric criteria for nutrients. In a memorandum issued in 2011, EPA stated that "it has long been EPA's position that numeric criteria targeted at different categories of water bodies and informed by scientific understanding of the relationship between nutrient loadings and water quality impairment are ultimately necessary for effective state programs." To this end, EPA has provided 30 states with technical assistance for numeric nutrient criteria development through its Nutrient Scientific Technical Exchange Partnership and Support Program. To date, 23 states have adopted numeric criteria into their water quality standards for nitrogen and/or phosphorus for at least one of their water bodies. In 2013, EPA outlined barriers to numeric nutrient criteria implementation and actions to help states address them. The barriers included, among other things, an inability to reduce nonpoint source loads of nitrogen and phosphorus and problems implementing water-quality-based limits. 
EPA has also emphasized the need to focus on reducing nutrients from all sources—both point and nonpoint sources. Under the CWA, EPA has authority to regulate discharges from point sources. However, the CWA does not authorize EPA to regulate nonpoint sources. EPA can influence activities of nonpoint sources only through use of grants and funding—such as CWA Section 319, which addresses nonpoint source pollution through state-run nonpoint pollution management programs—and related technical assistance. Through such programs, states may, for example, ask farmers or ranchers to use alternative methods in their operations to prevent fertilizers from reaching streams and may provide funds to help them install on-farm pollution management systems or practices. In its document addressing barriers to numeric nutrient criteria, EPA proposed actions to address them, including continuing to collaborate with the U.S. Department of Agriculture to leverage resources for conservation practices and to better quantify the environmental results of best management practices and other efforts, continuing to implement the Section 319 grant program, and addressing the challenges of manure management by working with large animal growers and poultry integrators to develop sustainability agreements and practices that reduce nutrient pollution. 
Some observers argue that the voluntary nature of controlling nonpoint sources is a key challenge in developing and implementing TMDLs, a primary tool that states are employing to address nutrient pollution. Farming and forestry groups have long been concerned about how their activities might be addressed in TMDLs and whether they might be subject to CWA regulation of some sort, even though the act does not provide EPA with regulatory authority over nonpoint sources. Municipalities and industries contend that regulating only point sources imposes disproportionate requirements on their operations, especially in waters that are impaired both by point and nonpoint sources.
subsections: section_title: Federal Financial Assistance
paragraphs: Recognizing that a critical role for EPA in addressing nutrient pollution is supporting watershed-based efforts at the state and local level, in its 2016 memorandum, the agency stated that the Office of Water would continue to provide financial assistance to states through CWA Section 106 and Section 319 grant programs and the Clean Water State Revolving Fund (CWSRF) Program, as well as Section 604(b) planning grants, Wetland Program Development grants, and grants targeted toward specific geographic locations, such as the Chesapeake Bay, Great Lakes, and other water bodies. The President's FY2019 budget request for EPA proposes that funding for these programs, with the exception of the CWSRF, be eliminated or significantly reduced (see Table 8 ). The proportion of funds provided to nonpoint source pollution projects through the CWSRF program is relatively minor compared to the amount provided to publicly owned treatment works for infrastructure projects. As reported by EPA, 96% of the cumulative assistance provided through the CWSRF as of 2016 has been provided to publicly owned treatment works; only 4% was provided to nonpoint source pollution projects and National Estuary Program projects. It is unclear how, considering EPA's long-standing emphasis on using these programs to address nonpoint source pollution, the FY2019 budget would support the goals of the agency in its efforts to reduce nutrient pollution, and ultimately reduce the occurrence and frequency of HABs.
 Table 8 presents a comparison of the President's FY2019 budget request with the FY2016-FY2018 enacted appropriations for selected grants and programs referenced above that include funding support for addressing nonpoint source pollution. These grants and programs are funded within the EPA State and Tribal Assistance Grants and the Environmental Programs and Management appropriations accounts.
section_title: Research Gaps
paragraphs: In addition to the challenges of reducing nutrient pollution contributing to HABs, scientists widely recognize key research gaps that hinder the ability to prevent, predict, minimize, and suppress HABs. In reauthorizing HABHRCA in 2014, as discussed above, Congress directed NOAA—through the IWG-HABHRCA—to prepare a comprehensive research plan and action strategy to address marine and freshwater harmful algal blooms and hypoxia. The February 2016 task force report includes a discussion of the key challenges in HAB and hypoxia management and discusses the many gaps in the research and management communities' knowledge of HAB and hypoxia events. Federal agencies—including USGS, EPA, and NOAA —and research efforts sponsored by these agencies cite similar gaps and areas needing continuing research. The following text box summarizes some of these key research areas. 
section_title: Legislation in the 115th Congress
paragraphs: Congressional interest in HABs has largely focused on funding further research and coordinating the efforts of federal agencies and their partners to study and address HABs. In the 115 th Congress, the Senate passed S. 1057 , which would, among other things, reauthorize HABHRCA for FY2019-FY2023, add the Army Corps of Engineers to the interagency task force, and allow the administrators of NOAA (marine) or EPA (freshwater) to declare a HAB or hypoxia event as an event of "national significance." Such a determination would prompt authority for the administrators to provide funding to the affected state or local government. A related bill, H.R. 4417 , has been introduced in the House.
The Senate also passed S. 129 , which would reauthorize the National Sea Grant Program and make funds available for HAB research through that program. The bill would authorize grants for university research on several targeted topics, including "the biology, prevention, and forecasting of harmful algal blooms." A related bill, H.R. 4306 , has been introduced in the House. 
The Great Lakes and Fresh Water Algal Bloom Information Act ( H.R. 1893 ) in the 115 th Congress would require NOAA to create an electronic database of research and information on the causes of, and corrective actions being taken with regard to, algal blooms in the Great Lakes, their tributaries, and other surface fresh waters and for other purposes. 
H.R. 3661 would establish a program to award prizes for the development of innovative, environmentally safe solutions for reducing, mitigating, and controlling harmful algal blooms and for other purposes.
Three bills have been introduced that would seek to address issues specific to Lake Okeechobee and the Florida Everglades:
H.R. 2137 seeks to address concerns arising from the HAB outbreak that occurred in Lake Okeechobee, FL, during the summer of 2016. Record rainfalls and an impending hurricane season prompted the U.S. Army Corps of Engineers to release water from the lake into rivers and estuaries in an attempt to keep the lake from overflowing. The releases occurred at a time when a lake-wide HAB was forming, allowing nutrients and algae to move downstream, eventually reaching area beaches and requiring beach closures and cleanups that had substantial impacts on the local and state economy. Florida's governor requested a federal state of emergency declaration, which the Federal Emergency Management Agency denied because it determined that supplemental federal assistance under the Robert T. Stafford Disaster Relief and Emergency Assistance Act was not considered appropriate for the event. H.R. 2137 would direct the President to treat a harmful algal bloom "caused by certain activities of the Federal Government" as an emergency for the purposes of the Stafford Act. H.R. 3665 would require the IWG-HABHRCA to prepare an assessment and a plan for reducing, mitigating, and controlling HABs and hypoxia in the Greater Everglades region, similar to what the working group has completed at a national level and for the Great Lakes region. H.R. 6645 would—similar to S. 1057 and H.R. 4417 —reauthorize HABHRCA but would also, like H.R. 3665 , require an assessment and action plan for the Everglades region.
section_title: Conclusion
paragraphs: Recent HAB events highlight the public health, economic, and environmental consequences that communities in the United States may continue to experience, perhaps on a more frequent basis. EPA, NOAA, and other federal agencies are working together to conduct important HAB-related research in an effort to close the gaps in the scientific and management community's understanding of how best to prevent, predict, minimize, and suppress HABs. EPA, states, and their partners are working to identify and restore waterbodies that are affected by HABs and the excess nutrients that contribute to their formation. 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 Administration's efforts to implement HABHRCA and other HAB-related authorities. 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. 
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 for regulation of nonpoint source pollution, arguing that point sources are disproportionately regulated and that nonpoint sources are the larger contributors to nutrient pollution. Instead of regulation, some argue that EPA and other federal agencies should continue to focus on collaborative, voluntary watershed-level efforts to address nonpoint source pollution that contributes to HAB formation and that Congress should ensure that financial assistance for these efforts continues. 
Controlling nonpoint sources of excess nutrients that contribute to HAB formation is challenging. They are diffuse and pervasive and often attributable to many sources and activities rather than a single cause. Yet, scientists generally agree that the current trends in overenriched waters and HAB events cannot be corrected without addressing nonpoint source nutrient pollution in a significant way and that controlling point sources alone is not enough. Given the consequences of HABs and the difficulty in controlling nonpoint sources of the nutrients that contribute to their formation, challenges and issues associated with HABs are likely to remain of interest to Congress.