For 20 years, the Natural Resources Defense Council has performed the white glove test on more than 3,000 beaches in the United States, focusing on water quality and health standards. This year, the nonprofit group had an extra challenge: to determine the effects of the oil spill on Gulf of Mexico beaches.

In its annual "Testing the Waters: A Guide to Water Quality at Vacation Beaches," the group expanded its focus to address the oil spill's footprint on gulf beaches, culling data from state Web sites, health officials and other authorities. As of the end of July, it determined that gulf beaches were closed or under advisory for 2,239 days, 10 times more than during the same period last year. Of about 250 monitored beaches along the coast, one in five were affected, including 16 of 20 Mississippi beaches, 16 of 180 in western Florida, 11 of 28 in Louisiana and 6 of 25 in Alabama. Texas beaches are unscathed.

"In the gulf, things are changing daily," said David Beckman, the NRDC's water program director, "but we know there's a lot of oil out there, and health officials need to diligently monitor the beaches."

To assist beachgoers, the organization created a comprehensive interactive map sprinkled with icons that provide up-to-date reports. For example, click on "Mobile County, Alabama," and a pop-up box shows an advisory for Dauphin Island Public Beach, plus a link for more info. The site is updated daily.

As in previous years, those headed to strands elsewhere may want to read the report before trading in their swimsuit for a hazmat suit. Based on government monitoring reports from 2009, the NRDC determined that last year (before the spill), pollution and contaminants resulted in 18,682 closures and advisory days, a 7 percent rate of health standards violations that has not budged since 2007.

"There is no clear trend that we are making progress, because of the runoff problem," Beckman said.

By region, the study found the dirtiest bodies of water to be the Great Lakes; the cleanest, in the Southeast and on the Delmarva Peninsula.

To further educate the swimsuited masses, the group also assigned stars to 200 of the most popular beaches, based on water cleanliness and monitoring and public notification practices. The organization has compiled a database at www. with more information.