Tar balls? A sheen of crude? Oil mousse? Amateur hour. The real villains of America’s beaches are not the scattered and dissipating messes from the Deepwater Horizon disaster, but the nationwide and relentless releases of disease-causing pathogens—human and animal feces—that reach the shorelines from storm runoff and sewage overflows. In its 20^th annual report on the water quality at America’s beaches, the Natural Resources Defense Council finds that “from stomach-turning pathogens to dangerous oil slicks, America’s beaches continue to suffer from pollution that can make people sick, harm marine life and destroy coastal economies,” said the NRDC’s David Beckman.

Before heading to a beach this weekend—on the Atlantic, the Pacific, the Gulf of Mexico, or the Great Lakes—be sure to check how it fares on measures of bacteria in the water (which come from human and animal waste), on testing that water (some beaches take water samples more frequently than others), and on posting advisories so that people can decide that a day swimming in fecal matter isn’t quite the weekend outing they had in mind. The ratings of popular beaches, arranged by state, are here.

All the data come from government records from 3,000 beaches, including water samples and beach closings or advisories (the latter being issued when bacterial levels in the water are high enough to warn the public about but do not exceed state or federal limits). In 2009, there were 18,682 closing and advisory days. That compares with 2,239 such days in the gulf region from the BP gusher.

The worst of the popular beaches were in Florida (Ben T. Davis North, Dixie Belle Beach, Monument Beach, Navarre Park, Quietwater Beach, Simmons Park and Treasure Island Beach), Maine (Old Orchard Beach, Long Sands Beach and Short Sands Beach), Mississippi (Courthouse Road Beach, Edgewater Beach and Front Beach), North Carolina (one section of Nags Head), New York (Hamlin Beach State Park, Orchard Beach, Robert Moses State Park Beach, and sections of Rockaway Beach and Coney Island), Rhode Island (Narragansett Town Beach), and South Carolina (Myrtle Beach, South Carolina State Park and Campground, Springmaid Beach and Surfside Beach).

Good news: 2009 saw an 8 percent decrease in closing and advisory days at U.S. beaches (though most of the East Coast and the entire Gulf Coast experienced more closings and advisories). Bad news: much of that can be attributed to the fact that budget cuts have forced beaches in southern California to cut back on water-quality monitoring. What you don’t know about can’t hurt you?