Bacterial contamination from stormwater runoff and sewage helped make 2011 one of the worst years in more than two decades for health-related closings and warnings at U.S. beaches, a major environmental group says.

The Natural Resources Defense Council’s annual assessment, released Wednesday, analyzes government data from more than 3,000 testing locations nationwide. It found that water quality at America’s beaches remained largely stable last year, with 8 % of water samples violating public health standards, the same as the previous year.

But there were 23,481 closing and advisory days in 2011, the third-highest level since NRDC began compiling their reports in 1990. That represented a 3% drop from 2010, which marked the second-highest number of closings and advisories since the group started its surveys. (The worst year, according to the NRDC, was 2006 with 25,643 closing or warning days.)

The Great Lakes region had the highest violation rate of beachwater standards - 11% of samples in 2011 - while the Mid-Atlantic’s Delmarva region had the lowest, with 4%. Individual states with the highest violation rates of reported samples were Louisiana (29%), Ohio (22%), and Illinois (12 %). States with the lowest rates of contamination last year - just 1% - were Delaware and New Hampshire.

For the first time this year, the NRDC has mapped more than 6,000 beaches nationwide, providing monitoring, closing and advisory information for more than half of them.

The searchable map includes a dozen beaches that earned the group’s five-star rating for violating health standards less than 5% of the time and for following such best practices as testing more than once a week and posting advisories online as well as at the beach. They include:

  California’s Newport, Huntington State and Bolsa Chica
  Alabama’s Gulf Shores Public Beach and Gulf State Park Pavilion
  Delaware’s Dewey Beach
  Maryland’s Ocean City Beach
  Minnesota’s Park Point Franklin Park and Lafayette Community Club Beach>
  New Hampshire’s Hampton Beach State Park and Wallis Sands
  Texas’ South Padre Island

On the flip side, 15 “repeat offenders” stood out for persistent contamination problems over the past five years. They include portions of:

  California’s Avalon and Doheny State Beach
  Illinois’ Winnetka Elder Park Beach, North Point Marina and North Beach
  Louisiana’s Constance, Gulf Breeze, Little Florida, Long and Rutherford
  New Jersey’s Beachwood Beach West
  New York’s Woodlawn and Ontario
  Ohio’s Euclid State Park and Villa Angela State Park
  Wisconsin’s South Shore Beach

Beachwater pollution nationwide causes a range of waterborne illnesses in swimmers including stomach flu, skin rashes, pinkeye, ear, nose and throat problems, dysentery, hepatitis, respiratory ailments, neurological disorders and other health problems. For senior citizens, small children and people with weak immune systems, the results can be fatal.

According to the NRDC, the Environmental Protection Agency’s proposed updates to federal water quality standards - due to be finalized this fall - “miss a critical opportunity to better protect beachgoers from the dangers of swimming in polluted waters,” and would put 1 in 28 swimmers at risk of getting a gastrointestinal illness.

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By Laura Bly, USA TODAY