A major farmers group filed a federal lawsuit on Monday to block the U.S. Environmental Protection Agency's most aggressive effort yet to clean the polluted Chesapeake Bay watershed, saying the costs of the cleanup will devastate farms and possibly drive them from the region.

The complaint filed by the American Farm Bureau Federation and one of its members, the Pennsylvania Farm Bureau, in a federal court in Harrisburg said EPA's plan cannot be legally enforced because its methods of determining the bay's pollution from nitrogen, phosphorous and sediment are flawed.

The groups also said that states, not the EPA, can enforce a so-called pollution diet and that the agency's process for determining a pollution diet for the bay moved too fast and did not allow public participation.

The Chesapeake Bay Foundation, which monitors pollution levels, blasted the farmers group, saying it was a "disappointing example of ... a high-powered lobbying group intent on misrepresenting the facts and frustrating the process of cleaning up the bay and its rivers."