No single source of pollution has contaminated the Chesapeake Bay over the years. If the nitrogen, phosphorus and sediment that have fouled its waters came from one place — a handful of urban wastewater treatment plants, for example — the problem would be relatively easy to correct.

But the reality is that most every human activity — from where we build our shopping centers to how we commute or choose to dispose or our trash — has consequences for water quality. Cleaning up the Chesapeake Bay and its tributaries, therefore, requires a broad and unrelenting approach to reduce human impact across the region.

That's why it's so discouraging to learn that the farm community is once again looking to find ways to exempt itself from more stringent pollution standards that might help revive the Chesapeake Bay. While farmers embrace voluntary guidelines and government programs that give them money to conserve or reduce pollution, they are not so enchanted by the prospect of a government agency setting and enforcing standards.

Such is the case with legislation sponsored by Maryland Sen. Benjamin L. Cardin that would put the force of law behind President Obama's efforts to clean up the Chesapeake Bay. The measure gives the U.S. Environmental Protection Agency authority to tighten a broad variety of pollution controls and hold polluters more accountable for the bay's condition.

But the agricultural community much prefers the competing approach championed by Representatives Tim Holden (D-Pa.) and Bob Goodlatte (R-Va.) that would shield farmers from more stringent regulations, essentially exempting those who have already adopted basic conservation plans. In a written statement, the American Farm Bureau Federation last week called the Holden-Goodlatte bill "reasonable" while other approaches (presumably those backed by Senator Cardin and Baltimore's Rep. Elijah Cummings) "would spell the end of agriculture for many farm families."

The farm bureau's position implies that agriculture's current efforts on behalf of a cleaner Chesapeake are sufficient, which, of course, they are not. The EPA estimates that farming is responsible for 32-38 percent of the nitrogen that pours into the bay, most of it from manure and chemical fertilizers. That's more nitrogen then all the region's sewage treatment plants combined. And some fear the Holden-Goodlatte bill would ultimately reduce the EPA's existing Clean Water Act authority to control farm-related pollution.

Environmentalists are not interested in killing family farms. Better to keep land in farming than to see it transformed into strip malls and tract homes. When farms curb their pollution — planting cover crops, keeping livestock out of streams, and reducing use of pesticides to name a few approaches — the result is not only cleaner water but often a more profitable farm.

Exempt agriculture, and the result will be more of the status quo, a gradual decline in bay water quality as excess nutrients and sediment lead to algae blooms, low dissolved oxygen levels and a continued loss of aquatic wildlife and habitat.

Farmers don't deserve to be handed the full burden for a cleaner Chesapeake Bay. The Cardin bill also directs more money to be spent for farm conservation and urban storm water run-off, arguably the two most neglected sources of pollution. But farmers must be willing to do their fair share or else there's little hope for the future of the nation's largest estuary.