NEW YORK, June 27 (UPI) -- For the third consecutive year, U.S. beaches experienced more than 20,000 closing and advisory days due to polluted water, an environmental group says.

The 23rd annual beach water quality report released by the Natural Resources Defense Council found 80 percent of the closings and advisories were issued because testing revealed bacteria levels in the water violated public health standards, confirming serious water pollution persists at many U.S. shores.

The primary known cause of this pollution is massive storm water runoff and sewage, the report said.

"Sewage and contaminated runoff in the water can spoil a family vacation real fast, turning a day of lounging at the beach into a day at the doctor's office with a sick child," Jon Devine, NRDC's senior attorney, said in the statement. "It's no surprise that pollution in the waves is bad for business in beach communities. Our government leaders can help support local economies and salvage countless summer getaways nationwide by tackling one of the principal sources of these problems -- storm water runoff."

The researchers analyzed the latest beach water testing data results from the U.S. Environmental Protection Agency and state beach coordinators at more than 3,000 beach testing locations nationwide.

Thirteen beaches had exceptionally low violation rates and strong testing and safety practices last year. There were:

-- Alabama: Gulf Shores Public Beach in Baldwin County.

-- Alabama: Gulf State Park Pavilion in Baldwin County.

-- California: Bolsa Chica Beach in Orange County.

-- California: Newport Beach in Orange County.

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Untreated sewage closed U.S. beaches for 20,000 days