The U.S. Congress should give farmers more than $6 billion a year to help them restore wetlands and prevent agricultural waste from polluting the nation’s waterways, according to American Rivers and Environmental Defense. They said yesterday that nearly half of the country’s bays are too polluted for fishing and swimming because of fertilizer and manure runoff from farms and ranches. The nation’s most polluted bay areas include the Chesapeake Bay, San Francisco Bay, and the northern Gulf of Mexico.