How the Clean Water Act Regulates U.S. Waterways and Pollution

When American Rivers Were So Polluted They Caught Fire

On June 22, 1969, the Cuyahoga River in Cleveland, Ohio, caught fire for at least the thirteenth time. An oil slick and industrial debris on the river's surface ignited, sending flames five stories high. The fire lasted only 30 minutes, but the photograph—published weeks later in Time magazine—became the defining image of American environmental degradation. Three years later, Congress passed the Federal Water Pollution Control Act Amendments of 1972, known universally as the Clean Water Act (CWA), establishing the framework that still governs U.S. water quality regulation today.

The Act's Ambitious Goal

The CWA set two objectives that were radical for their time: eliminate the discharge of pollutants into navigable waters by 1985, and achieve water quality sufficient to protect fish, shellfish, and wildlife and provide for recreation by 1983. Neither deadline was met. But the law fundamentally transformed American waterways. Before 1972, two-thirds of U.S. lakes, rivers, and coastal waters were unsafe for fishing or swimming. By 2020, that figure had been cut roughly in half.

The NPDES Permit System

The CWA's most powerful tool is the National Pollutant Discharge Elimination System (NPDES). Any facility that discharges pollutants from a "point source" into "waters of the United States" must obtain an NPDES permit. Point sources include pipes, ditches, channels, and any discrete conveyance.

• Permits set specific limits on the type and quantity of pollutants that can be discharged
• Limits are based on technology-based standards (what treatment technology can achieve) and water quality-based standards (what the receiving water body can absorb)
• Permits are issued for five-year terms and must be renewed
• The EPA administers the program nationally but has delegated permitting authority to 47 states
• Permit holders must monitor their discharges and submit regular reports—violations trigger enforcement actions

There are approximately 400,000 active NPDES permits in the United States. Major industrial facilities, municipal wastewater treatment plants, and concentrated animal feeding operations (CAFOs) account for the most significant discharges.

Point Source vs. Nonpoint Source: The Enforcement Gap

The CWA regulates point sources effectively. Nonpoint source pollution—the diffuse runoff from farms, construction sites, roads, and urban areas—is a different story entirely. The law does not require NPDES permits for nonpoint sources, relying instead on voluntary programs and state-managed best management practices.

Agricultural runoff—carrying fertilizers, pesticides, and animal waste—is the single largest source of water pollution in the United States today. Nitrogen and phosphorus from farm fields feed algal blooms that create oxygen-depleted "dead zones," including the annual Gulf of Mexico dead zone that covers roughly 15,000 square kilometers each summer.

TMDLs: The Pollution Budget

When a water body fails to meet water quality standards despite NPDES permits, Section 303(d) of the CWA requires states to establish a Total Maximum Daily Load (TMDL)—essentially a pollution budget. The TMDL calculates the maximum amount of a specific pollutant that a water body can receive and still meet quality standards, then allocates that budget among all contributing sources.

• Over 40,000 water bodies in the United States are listed as impaired under Section 303(d)
• Common pollutants triggering TMDL listings include sediment, pathogens, nutrients, and temperature
• TMDL development is slow—many states have backlogs stretching decades
• Enforcement of TMDL allocations on nonpoint sources remains largely voluntary
• The Chesapeake Bay TMDL (2010) is the largest and most ambitious, covering a six-state watershed

"Waters of the United States": The Definition War

No phrase in environmental law has generated more litigation than "waters of the United States" (WOTUS). The CWA applies to "navigable waters," defined as "waters of the United States." But how far does that extend? Major rivers? Tributaries? Wetlands adjacent to tributaries? Isolated ponds? Seasonal streams? Ditches?

Every administration since the 1980s has fought over the definition. The Obama administration's 2015 Clean Water Rule expanded WOTUS broadly. The Trump administration's 2020 Navigable Waters Protection Rule narrowed it dramatically. The Biden administration issued a replacement in 2023—which was then substantially overridden by the Supreme Court.

Sackett v. EPA (2023): The Game-Changing Ruling

In Sackett v. Environmental Protection Agency, the Supreme Court unanimously ruled that the EPA had exceeded its authority by regulating the Sacketts' property near Priest Lake, Idaho. But the justices split sharply on the broader legal standard. The majority opinion, written by Justice Alito, established that wetlands are covered by the CWA only if they have a "continuous surface connection" to a traditionally navigable water body.

• The ruling eliminated CWA jurisdiction over millions of acres of wetlands that lack a continuous surface connection to navigable waters
• Seasonal and geographically isolated wetlands lost federal protection
• The EPA estimated that the ruling reduced CWA-covered wetlands by approximately 50%
• States can still regulate these wetlands under state law, but fewer than half have strong independent wetland protections

Section 404: Wetland Fill Permits

Section 404 of the CWA regulates the discharge of dredged or fill material into wetlands and other waters. The Army Corps of Engineers issues Section 404 permits, with EPA oversight and veto authority. This provision has been the primary federal tool for protecting wetlands from development since the 1970s, preventing the draining and filling of marshes, bogs, and swamps for agriculture and construction. After Sackett, the reach of Section 404 is significantly narrower, and the long-term consequences for wetland loss remain to be seen.

This article is for informational purposes only and does not constitute legal advice.