Surprising as it may seem, the 1972 Clean Water Act — whose stated goal is fishable and swimmable waters for all — has always exempted most agricultural pollutants from regulation. This nearly 50-year-old policy prevents the federal government from employing a polluter pays approach — a method that has proved successful in tackling industrial and municipal sources of water pollution, including raw sewage, toxic chemicals and industrial byproducts. Instead, the Clean Water Act relies on voluntary action from farmers. In effect, farmers are requested to change their behavior and voluntarily raise their own cost of production, even when their competitors do not, to fix a water quality problem that often occurs far downstream.

Farmers could do more, but competitive realities limit even those producers with the best intentions. Reducing fertilization can help, but even when carefully applied, some fertilizer inevitably leaves fields and accumulates in waters. Costlier changes — such as planting a cover crop in the fall to prevent nutrient loss over the winter, restoring wetlands and streams, planting vegetation at the edges of streams and managing drainage — would help. Currently the only option is for taxpayers to pay them to make these changes.

Last year, taxpayers spent five billion dollars to take land out of production and support conservation practices. This may sound like a lot, but five times that was spent on industrial and municipal pollution control, much of it paid for by the businesses and cities that generate pollution. Even at current levels of taxpayer support, the state of Iowa reports that additional conservation practices are needed on the bulk of its 25 million acres to solve its contribution to the Gulf dead zone.

What’s more, the E.P.A. reports that 150,000 miles of streams and nearly five million acres of lakes across the country remain impaired from nutrients. And while most Americans drink water from publicly filtered sources, nearly 14 percent drink water from private wells with no required monitoring or treatment requirements, making them vulnerable to nitrate pollution . Blue baby syndrome, for example, is a rare but well-known problem when infants ingest nitrates. Recent studies suggest that nitrates in drinking water are associated with increased risks of colorectal cancer, thyroid disease and birth defects.

Although the federal government cannot regulate agriculture under the Clean Water Act, states can. They are free to impose taxes, require permits and regulate in any way they see fit. A few have taken action. Iowa, Maryland, Minnesota, Vermont and Wisconsin ban the use of manure fertilizer on frozen ground, a practice known to prevent runoff. More ambitiously, in 1995 Florida required conservation actions in the Everglades Agricultural Area such as storm water management, erosion controls and more precise fertilizer application on farms. Reductions in phosphorus pollution occurred promptly, and the annual average decrease of 50 percent has exceeded the regulation’s goals. T hough the area covers less than 5 percent of Florida agriculture, it demonstrates the compatibility of regulation and a successful agricultural industry.