(CBS) - Swimmers, take heed: Ten percent of water samples taken from U.S. coastal and lake beaches fail to meet safety standards set by the U.S. Environmental Protection Agency, a new report finds.
"There can be hidden dangers lurking in many of our waterways in the form of bacteria and viruses that can cause a great inventory of illnesses like dysentery, hepatitis, stomach flu, infections and rashes," Steve Fleischli, water program director for the Natural Resources Defense Council, said at a Wednesday press conference.
Of nearly 3,500 samples taken annually at beaches around the country, Great Lakes beaches have the highest failure rate, with excessively high bacteria levels, the defense council said.
This finding confirms that water pollution caused by storm-water runoff and sewage overflows persists at many U.S. beaches, the agency said.
Storm-water runoff often includes trash, chemicals, oil and animal and human waste as well as bacteria and viruses.
"It's really all of our urban slobber going untreated into local waterways," Fleischli said.
Still, the agency singled out 35 popular "superstar" beaches that have excellent water quality.
Each of these met national water quality standards 98 percent of the time over the past five years. They include:
Delaware: Dewey Beach-Swedes in Sussex County
Florida: Bowman's Beach in Lee County
Georgia: Tybee Island North in Chatham County
Massachusetts: Singing Beach in Essex County
New Jersey: Stone Harbor at 96th St. in Cape May County
The 17 "repeat offenders" that continue to have serious water pollution problems include:
California: Malibu Pier, 50 yards East of the pier, in Los Angeles County
Indiana: Jeorse Park Beach in Lake County
Massachusetts: Cockle Cove Creek in Barnstable County
Maine: Goodies Beach in Knox County
New Jersey: Beachwood Beach in Ocean County
New York: Main Street Beach in Chautauqua County
In the Great Lakes, 13 percent of samples failed to meet federal public health standards, the researchers said.
Other regions with excessively high bacteria in swimming water samples include: the Gulf Coast (12 percent), New England (11 percent), the western coast (9 percent), New York and New Jersey coasts (7 percent), and the southeast (7 percent).
States with the highest failure rates include: Ohio (35 percent), Alaska (24 percent) and Mississippi (21 percent).
For cleaner water, try the Delmarva Peninsula area on the East Coast, where 4 percent of samples failed the test.
Three states had a failure rate of just 3 percent: Delaware, New Hampshire and New Jersey, the researchers found.
As many as 3.5 million Americans are sickened from contact with raw sewage overflows each year, according to the EPA.
"The elderly and little kids are most likely to fall prey to contamination in the water because of their weaker immune systems," Fleischli said.
"Children are also more likely to dunk their heads under the water or swallow water when swimming, both of which increase risk," he added.
Under the federal Beaches Environmental Assessment and Coastal Health (BEACH) Act, states must test beach water for bacteria. When bacteria levels are too high -- such as after a heavy rain -- beaches may be closed or people might be advised not to swim.
More than 10 trillion gallons of untreated storm water, including billions of gallons of untreated sewage, find their way into America's waterways each year, the EPA said. Historically, this is the largest known source of beach water pollution.
The best way to prevent beach water pollution, said the defense council, is to invest in "smarter, greener infrastructure on land, like porous pavement, green roofs, parks, roadside plantings and rain barrels."
Such improvements enable rain to evaporate or filter into the ground instead of being carried from dirty streets to beaches.
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