The Clean Water Act (CWA) is the main federal law in the United States that controls water pollution. Its goal is to improve and protect the chemical, physical, and biological health of the nation’s water systems. It recognizes that states have the primary responsibility for handling pollution and provides them with support, including money for publicly owned wastewater treatment facilities. It also works to protect wetlands.

The Clean Water Act was one of the first and most important environmental laws in the United States. The law and its rules are mainly managed by the U.S. Environmental Protection Agency (EPA) with help from state governments. However, some parts of the law, such as those about filling or dredging water areas, are handled by the U.S. Army Corps of Engineers. The rules for the law are written in parts of the Code of Federal Regulations (40 C.F.R.) called Subchapters D, N, and O (Parts 100–140, 401–471, and 501–503).

The official name of the law is the Federal Water Pollution Control Act. The first version of this law was passed in 1948, but it was completely rewritten in 1972 as the Federal Water Pollution Control Act Amendments of 1972. Later changes were added through laws such as the Clean Water Act of 1977 and the Water Quality Act of 1987.

The Clean Water Act does not directly deal with pollution in groundwater. Groundwater protection is covered by other laws, including the Safe Drinking Water Act, the Resource Conservation and Recovery Act, and the Superfund Act.

Background

Drinking water can become polluted not only at the source but also during transport through pipes and other parts of the system. Sources of water pollution include naturally found chemicals like arsenic, radon, and uranium, as well as human activities such as using fertilizers and pesticides, manufacturing, and sewage overflows. Contaminated water can lead to health issues such as stomach and intestinal problems, reproductive system illnesses, and brain and nerve disorders. People who are especially vulnerable include infants, young children, pregnant women, the elderly, and those with weakened immune systems due to conditions like AIDS, chemotherapy, or transplant medications.

Stomach and intestinal problems include conditions such as constipation, irritable bowel syndrome, and colitis. Children and the elderly are most at risk for these issues. A study in Philadelphia found that poor water quality up to 9 to 11 days before a hospital visit was linked to more hospital admissions for stomach and intestinal problems. This connection was stronger in people over 75 than in those aged 65–74. This example shows that some people in the United States may still face risks of waterborne stomach and intestinal illnesses despite current water treatment practices.

Reproductive system illnesses refer to any health issues affecting the reproductive system. New research from Brunel University and the University of Exeter supports the link between water pollution and increased male fertility problems. The study identified chemicals in polluted water that act as antiandrogens, which interfere with the male hormone testosterone and reduce fertility.

Brain and nerve disorders are diseases affecting the brain, spine, and connecting nerves. A study of over 700 people in California’s Central Valley found that individuals who likely drank water from private wells near fields treated with insecticides had a higher risk of Parkinson’s disease. Private wells are often not monitored for contaminants and are usually shallow, making them more likely to contain pesticides. These chemicals can harm developing brains during pregnancy or infancy, leading to brain and nerve disorders later in life. A study by UCLA professor Beate Ritz found that people with Parkinson’s were more likely to have used private well water and had used it for an average of 4.3 years longer than those without the disease.

Water pollution harms aquatic environments, including rivers, coasts, and oceans. Industrial waste can contain chemicals, drugs, and heavy metals. Untreated sewage and industrial waste can reduce oxygen levels, harming fish and other animals. Natural materials like leaves and human-made chemicals can make water cloudy, blocking light and clogging fish gills. Too many nutrients can cause algae and bacteria to grow, using up oxygen and damaging the environment. Heat from power plants and factories can lower oxygen levels, harming aquatic life and reducing biodiversity.

Waters protected

In the 2023 Supreme Court case Sackett v. EPA, the court decided that only "relatively permanent" waters, such as streams, oceans, rivers, and lakes, that are connected to "navigable waters," and wetlands that are "indistinguishable" from such waters, are protected under the Clean Water Act (CWA).

The 1972 CWA often uses the term "navigable waters," which is defined as "waters of the United States, including the territorial seas." Rules made to explain the law have included features like intermittent streams, playa lakes, prairie potholes, sloughs, and wetlands as "waters of the United States." In 2006, in Rapanos v. United States, a group of Supreme Court justices, led by Justice Antonin Scalia, said "waters of the United States" includes only "relatively permanent, standing or continuously flowing bodies of water 'forming geographic features' described as 'streams, oceans, rivers, and lakes.'" Justice Anthony Kennedy, in a separate opinion, said the term includes wetlands that have a "significant nexus" to traditionally defined navigable waters.

After Rapanos, the EPA and the U.S. Army Corps of Engineers tried to clarify which waters are protected under the CWA using the 2015 Clean Water Rule. This rule was based on Justice Kennedy’s definition of "significant nexus" but became very controversial.

In 2023, the Supreme Court rejected the "significant nexus" test in Sackett v. EPA and created a new, stricter definition for which waters are covered under the CWA. This new rule limits the scope of federal Clean Water Act regulation.

Pollution control strategy

The Clean Water Act (CWA) introduced the National Pollutant Discharge Elimination System (NPDES), a permit system to control pollution from specific sources. These sources include:

• Industrial facilities (such as manufacturing, mining, shipping, oil and gas extraction, and service industries).
• Municipal governments (like sewage treatment plants) and other government facilities (such as military bases).
• Some agricultural facilities, such as animal feedlots.

Point sources must have an NPDES permit to release pollutants into surface waters. The system is managed by the Environmental Protection Agency (EPA) and state environmental agencies. EPA has allowed 47 states to issue permits directly to dischargers. The CWA also allows tribes to issue permits, but no tribes have been authorized by EPA. In other states and territories, permits are issued by EPA regional offices. (See Titles III and IV.)

Before 1972, Congress let states set water quality standards to limit pollution based on the characteristics of specific water bodies. However, these standards only applied to interstate waters, and the science to support them was not fully developed. This system was not effective, and no permit system existed to enforce requirements. The 1972 CWA added a permit system and required technology-based limits on pollution.

In the 2020 Supreme Court case County of Maui v. Hawaii Wildlife Fund, the Court said some discharges are not point sources but may be the "functional equivalent of a direct discharge" to navigable waters, such as injecting wastewater into groundwater wells. At the time of the decision, EPA had not created rules for these cases, and the Court told EPA to work with courts to define such discharges. The Court said this would depend on how far pollutants travel, how long they take to reach water, the materials they pass through, and how much pollution reaches navigable waters. In 2021, a Hawaii court ruled that Maui County’s sewage injection into groundwater was a "functional equivalent of a direct discharge" and required an NPDES permit.

The 1972 CWA required technology-based standards for pollution from point sources. EPA creates these standards for groups of dischargers, based on pollution control technology performance, not on the specific conditions of water bodies. Congress aimed to create fairness by setting a basic national standard for all facilities in a category using "Best Available Technology." This standard is the minimum requirement in permits. If a national standard is not enough to protect water quality in a specific area, water quality standards may be used, and permits will include stricter limits.

The 1972 CWA allowed continued use of water quality-based standards, working alongside technology-based standards. After applying technology-based standards to a permit, if water quality is still poor, the permit agency may add stricter water quality-based limits. Water quality standards include four parts: 1) Designated uses (such as drinking water or recreation), 2) Water quality criteria (limits on pollution levels), 3) Antidegradation policy, and 4) General policies.

States and federally recognized tribes must define appropriate uses for water bodies in their areas. These uses consider public water supply, fish and wildlife protection, recreation, and other needs. Suitability is determined by physical, chemical, and biological features, as well as geography, scenery, and economic factors. If standards show that current uses are not met, states or tribes must update them. For water bodies not designated for "fishable/swimmable" uses, a "Use Attainability Analysis" must be done. These analyses are reviewed every three years to check for new information that might require changes.

States and tribes protect water quality by using EPA-published criteria, adjusting them for local conditions, or using other scientifically valid methods. Numeric criteria set pollution limits based on known toxicity. Narrative criteria describe rules to limit harm to aquatic life. Biological criteria describe the types and numbers of species in a water body. Nutrient criteria prevent over-enrichment, and sediment criteria describe conditions to avoid harmful effects.

Water quality regulations include an anti-degradation policy requiring states and tribes to create a three-tiered program. Tier 1 protects all surface waters by maintaining current uses and water quality. Tier 2 protects water bodies that already support "fishable/swimmable" uses. Tier 3 protects "outstanding national resource waters" (ONRWs), which are high-quality waters with ecological importance.

States and tribes also adopt general policies, such as mixing zones, variances, and low flow policies, which are reviewed and approved by EPA. Mixing zones are areas near discharges where pollution is diluted. Variance policies temporarily relax standards and are reviewed every three years. Low flow policies address water quality during low water levels.

Major statutory provisions

This Act has six titles.

Title I explains the goals and policies of the Act and includes authorizations for research and pollution control programs. Some programs from the 1972 law, such as section 104 research programs, section 106 pollution control programs, and the Chesapeake Bay Program, are still active. Other programs no longer receive funding and have been stopped.

Title II helps cities build or expand sewage treatment plants, also called publicly owned treatment works (POTW). The 1972 Clean Water Act allowed federal funds to cover 75% of project costs, with state and local funds covering the remaining 25%. In 1981, Congress reduced the federal funding share to 55% for most grants.

The construction grant program was replaced in 1987 by the Clean Water State Revolving Fund (see Title VI). However, some local utilities still received special purpose project grants directly from Congress through a process called "earmarking."

Section 301 of the Act bans discharges into U.S. waters except with a permit. Permit programs are discussed in Title IV. Recreational vessels are not required to have permits, but their operators must follow Best Management Practices to control discharges. More information about ship pollution regulations can be found in the relevant section.

Under the 1972 Act, the Environmental Protection Agency (EPA) began setting technology-based standards for municipal and industrial sources:
– Municipal sewage treatment plants must meet secondary treatment standards.
– Effluent guidelines (for existing sources) and New Source Performance Standards (NSPS) are set for industrial facilities that discharge directly into surface waters.
– Categorical Pretreatment Standards are set for industrial users who send waste to POTW. These standards apply to both existing and new sources. There are 28 categories with pretreatment standards as of 2023.

As of 2023, effluent guidelines and categorical pretreatment standards have been published for 59 categories. These regulations apply to between 35,000 and 45,000 facilities that discharge directly into water, 129,000 facilities that discharge to POTW, and construction sites. These rules help prevent the discharge of nearly 700 billion pounds of pollutants each year. EPA has updated some categories and added new ones since their creation.

Secondary treatment standards for POTW and effluent guidelines are enforced through NPDES permits (see Title IV). Categorical pretreatment standards are usually enforced by POTW through permits issued to industrial users.

The Clean Water Act requires states to monitor their water bodies and set Water Quality Standards (WQS) for them. WQS are rules that set specific pollutant limits for individual water bodies, such as rivers, lakes, and streams. States set WQS by defining the uses of the water body (e.g., recreation, water supply) and applying water quality criteria (numeric limits and narrative requirements) to protect these uses. Each state also creates an antidegradation policy to protect high-quality waters and existing uses.

If a state fails to set WQS, EPA must create standards for that state.

Water bodies that do not meet WQS with technology-based controls alone are listed under section 303(d). These water bodies require a Total Maximum Daily Load (TMDL), which calculates the maximum amount of a pollutant a water body can receive while still meeting WQS. A TMDL is determined after studying the water body and its pollutant sources. It includes a Waste Load Allocation (WLA), Load Allocation (LA), and Margin of Safety (MOS). After a TMDL is created, an implementation plan is developed to reduce pollution and bring the water body into compliance.

Once a TMDL is issued, NPDES permits for facilities discharging to the water body are updated to meet the WLA (see Title IV). Creating WQS and TMDLs is a complex process that requires significant resources from state agencies.

More than half of U.S. streams and rivers still do not meet water quality standards. Surveys show that about 70% of lakes, ponds, and reservoirs are impaired, and over 70% of coastlines and 90% of surveyed ocean and coastal areas are also impaired.

The National Water Quality Inventory Report is the main way to assess the quality of rivers, lakes, streams, ponds, estuaries, coastal waters, and wetlands in the U.S. States and other jurisdictions (such as territories and tribes) use their water quality standards to conduct assessments. The report is sent to Congress to show compliance with water quality standards. It identifies water quality problems, lists impaired water bodies, and highlights non-point sources of pollution. Every two years, states must submit reports to EPA that describe water quality conditions and include a full analysis of the social and economic costs and benefits of meeting the Act’s goals.

Under section 309, EPA can issue administrative orders against violators and seek civil or criminal penalties when needed:
– For a first offense of criminal negligence, the minimum fine is $2,500, with a maximum of $25,000 per day of violation. A violator may also be jailed for up to one year. A second offense could result in a maximum fine of $50,000 per day.
– For knowing endangerment, which puts someone in immediate danger of death or serious harm, a fine of up to $250,000 and/or 15 years in prison for an individual, or up to $1,000,000 for an organization, may be issued.
– For civil violations, EPA can seek up to $66,712 per violation per day.

States authorized by EPA to manage the NPDES program must enforce permit requirements under their own laws.

Military bases, national parks, and other federal facilities must follow CWA rules.

Section 316 sets standards for thermal pollution and cooling water intake structures, such as fish screens. These standards apply to power plants and other industrial facilities.

The 1987 amendments created the Nonpoint Source Management Program under CWA section 319. This program gives grants to states, territories, and Indian tribes to support projects that reduce nonpoint source pollution. Grant funding averaged $210 million annually from 2004 to 2008.

Congress

Recent developments

The Clean Water Act's area of influence, which includes the definition of "navigable waters" or "waters of the United States," has caused a lot of debate. Between the Supreme Court's 2006 decision in Rapanos v. United States and its 2023 ruling in Sackett v. EPA, several attempts to define "waters of the United States" failed.

After Rapanos, the Environmental Protection Agency (EPA) and the Army Corps of Engineers created a guidance document to explain how the Clean Water Act's jurisdiction would be determined. This guidance included parts from the Rapanos plurality test and Justice Kennedy's "significant nexus" test. However, many people believed this guidance did not work well. To address this, the Obama administration introduced the Clean Water Rule on June 29, 2015. This rule used Justice Kennedy's "significant nexus" test to regulate most water features through a case-by-case review. However, courts blocked the rule shortly after it was created.

The Trump administration then tried to create a new rule, the Navigable Waters Protection Rule, in April 2020. This rule mainly used Justice Scalia's test from Rapanos and included some parts of Justice Kennedy's "significant nexus" test. This effort was also blocked by courts.

Under President Joe Biden, the U.S. Army Corps of Engineers and EPA published a revised definition of "waters of the United States" on January 18, 2023. This definition restored rules from before 2015 and became effective on March 20, 2023. It relied mostly on Justice Kennedy's "significant nexus" test. However, courts blocked this rule within weeks of its release.

On May 25, 2023, the Supreme Court ruled in the second Sackett v. Environmental Protection Agency case. This decision limited the Clean Water Act's authority to only wetlands and waters that have a continuous surface connection to larger bodies of water, returning to Justice Scalia's definition from Rapanos. This means the EPA can no longer regulate water that is not connected to larger water bodies. Some estimates suggest this decision removed EPA oversight from about half of the waters it previously regulated. By directly defining "waters of the United States," the Supreme Court's Sackett decision ended the long-standing debate about the Clean Water Act's scope.

Earlier legislation

During the 1880s and 1890s, Congress asked the U.S. Army Corps of Engineers (USACE) to stop people from dumping or filling materials in the nation’s harbors, and this rule was strongly enforced. In 1899, Congress passed the Rivers and Harbors Act, which gave the Corps the power to control most things that blocked ships from moving, including dangers caused by waste materials. Part of this law, called Section 13 or the Refuse Act, is still used today. In 1910, USACE used the act to object to a planned sewer in New York City, but a court said that pollution control was the responsibility of states, not the federal government. At a meeting in 1911, William H. Bixby, the Corps chief, suggested that modern waste treatment systems and rules against dumping should be required or encouraged nationwide. Most legal experts believe the 1899 law did not address environmental harm from pollution, such as sewage or industrial waste. However, in the 1960s and 1970s, the law was used in some cases to support broader pollution control goals.

Some parts of the 1899 law have been replaced by later laws, including the 1972 Clean Water Act (CWA). Other important laws before the CWA include:

• The Public Health Service Act of 1912 increased the work of the U.S. Public Health Service to study problems like poor sanitation, sewage, and pollution.
• The Oil Pollution Act of 1924 banned intentionally pouring fuel oil into tidal waters and allowed USACE to arrest people who broke this rule. This law was replaced by the 1972 CWA, which limited the Corps’ role in pollution control to managing waste from dredging or filling.
• The Federal Water Pollution Control Act of 1948 created many water quality programs and gave some money to states and local governments. This law only applied to waterways between states, and the Public Health Service helped with funding and technical support.
• The Water Quality Act of 1965 required states to set water quality standards for waterways between states and allowed a new federal group, the Federal Water Pollution Control Administration, to set standards if states did not.

In 1970, when the Environmental Protection Agency (EPA) was created, it had limited power to protect U.S. waters. It could not create rules for waste water and only had general authority to require industrial companies to treat their waste.

The 1969 fire on the Cuyahoga River caused public anger and helped inspire the Clean Water Act. In December 1970, a federal grand jury investigation led by Ohio lawyer Robert Jones began, looking into water pollution caused by about 12 companies in northeastern Ohio. This was the first grand jury investigation of water pollution in the area. The U.S. Attorney General, John N. Mitchell, gave a press conference on December 18, 1970, talking about new pollution control lawsuits and announcing a lawsuit against the Jones and Laughlin Steel Corporation for releasing large amounts of cyanide into the Cuyahoga River near Cleveland. These and other legal cases helped shape the requirements for new laws. Some scholars disagree about the connection between the Cuyahoga River fire and the creation of the Clean Water Act.

Case law

• United States v. Riverside Bayview Homes, Inc. 474 U.S. 121 (1985). The Supreme Court supported the law's ability to regulate wetlands that mix with navigable waters. This decision was changed by the 2006 Rapanos case and the 2023 Sackett case.
• Edward Hanousek, Jr. v. United States (9th Cir. Court of Appeals, 1996; certiorari denied, 2000). In 1994, a backhoe operator accidentally hit a petroleum pipeline near railroad tracks, causing it to break and spill between 1,000 and 5,000 gallons of heating oil into the Skagway River. Edward Hanousek, Jr., the roadmaster, and Paul Taylor, the president of the company, were held responsible for the spill and convicted, even though they were not present during the operation.
• Solid Waste Agency of North Cook County (SWANCC) v. United States Army Corps of Engineers 531 U.S. 159 (2001). The court said the Clean Water Act does not apply to certain isolated intrastate waters and rejected the validity of the 1986 "Migratory Bird Rule."
• S. D. Warren Co. v. Maine Bd. of Env. Protection 547 U.S. 370 (2006). The Court ruled that state certification requirements under Section 401 apply to hydroelectric dams that are federally licensed and cause discharge into navigable waters.
• Rapanos v. United States 547 U.S. 715 (2006). The Supreme Court questioned federal control over the terms "navigable waters" and "waters of the United States." The Court rejected the claim that the U.S. Army Corps of Engineers had unlimited authority over water. The case did not create a clear rule for federal authority, but the Court rejected the government's idea that any wetland or water connected to navigable waters is under federal control.
• Northwest Environmental Advocates et al. v. EPA (9th Cir. Court of Appeals, 2008). Discharges from vessels are subject to NPDES permit requirements. See Ballast water regulation in the United States.
• Sackett v. Environmental Protection Agency, 566 U.S. 120 (2012). The Supreme Court ruled that an EPA compliance order under Section 309(a) of the Clean Water Act is a "final agency action" that can be reviewed by courts under the Administrative Procedure Act.
• National Cotton Council v. EPA (6th Cir. Court of Appeals, 2009). Discharges of biological pesticides and chemical pesticides that leave residue into waters of the United States are subject to NPDES permit requirements.
• Army Corps of Engineers v. Hawkes Co. 578 U.S. __ (2016). The Court ruled that a determination by the Army Corps of Engineers that land contains "waters of the United States" is a "final agency action," which can be reviewed by courts. This allows landowners to sue in court if the Corps determines that land contains waters of the United States.
• County of Maui v. Hawaii Wildlife Fund 590 U.S. __ (2020). The Court ruled that a NPDES permit is required for point sources or for non-point sources that are "functionally equivalent" to direct discharge, such as wastewater from injection wells that eventually reach the ocean, a navigable waterway.
• Sackett v. Environmental Protection Agency 598 U.S. __ (2023). The Supreme Court unanimously rejected the government's "significant nexus" test for federal jurisdiction under the Clean Water Act. A five-justice majority ruled that the Act applies at most to "relatively permanent waters" and wetlands that maintain continuous surface connection to such waters, with no clear boundary between wetlands and waters.

Effects

Since the Clean Water Act was passed in 1972, the goals set by Congress have not yet been fully achieved. These goals included:

• Making all U.S. waters safe for fishing and swimming by 1983;
• Stopping all water pollution discharge by 1985;
• Preventing the release of harmful amounts of toxic pollutants.

Today, more than half of U.S. streams and rivers, about 70% of lakes, ponds, and reservoirs, and 90% of surveyed ocean and coastal areas still fail to meet water quality standards. The reasons for these problems vary by location, but major causes include agriculture, industry, and communities (often through runoff from cities). Some pollution sources are hard to control with national rules.

However, since the 1972 law was passed, pollution levels in the United States have dropped significantly. The law has led to much cleaner waterways than before the law was created. Agriculture, industry, and communities still release waste into surface waters across the country, and many of these waters are used for drinking. In many areas, nutrient pollution (too much nitrogen and phosphorus) has become a major issue.

A 2008 article says the Clean Water Act has helped the environment a lot but needs changes to solve remaining pollution problems. A 2015 article agrees the law has worked well for controlling pollution from specific sources, like factories, but has not been as effective for pollution from less direct sources, such as farming or city runoff. It says the law needs updates to address current water quality issues.

A 2017 study found that most types of water pollution decreased between 1962 and 2001, but the rate of improvement slowed over time. The study suggests that water quality problems were even worse before the Clean Water Act. Some research has found that the costs of the Clean Water Act (including spending on construction grants) are higher than the benefits. An EPA study reached similar conclusions but noted that some benefits were not measured. A 2018 study said that estimates of the costs and benefits of water pollution control programs, including the Clean Water Act, are incomplete and do not clearly show whether the program has been beneficial overall.

Criticism

According to an article from the National Bureau of Economic Research, the Clean Water Act is one of the most hotly debated rules in U.S. history. The article states that it is unclear whether the Act has been effective or if water pollution has clearly decreased. A study from the 1990s noted these questions, saying, “As we reached the 20-year anniversary of the Clean Water Act, no complete analysis existed to answer basic questions: Are our rivers cleaner now than they were 20 years ago?”

Paul McCracken, who led the Council of Economic Advisers, called the Clean Water Act an “inefficient use of national resources that would not balance social and economic benefits.”

The Pacific Legal Foundation, a public interest law firm, said that unclear and broad definitions of “navigable waters” by the EPA and the U.S. Army Corps of Engineers have caused government overreach, sudden changes in rules, and misuse of authority. These concerns were supported by the Supreme Court, which unanimously rejected the EPA and the U.S. Army Corps of Engineers’ use of the “significant nexus test” in the second Sackett case.