New York’s beaches are being closed and put under warning more regularly in an attempt to limit swimmers’ exposure to sewage, according to a report released yesterday by the Natural Resources Defense Council.

State beaches were closed or put on advisory 1,547 days in 2007, compared to 1,280 days in 2007, and 827 days in 2005.

Most of the closings and advisories were pre-emptive attempts to limit beachgoers’ exposure to sewage overflows after rainfall, as a fraction of an inch of rain can overwhelm the sewage system and cause overflows. About 27 billion gallons of mixed rainwater and sewage are dumped each year into the New York Harbor, according to the council.

The report found that 11% of the water samples the council collected from New York beaches had bacteria contamination levels higher than the state’s standards, up from 10% in 2006.

In January, the City Council legislated to prevent runoff by developing “green infrastructure” such as permeable pavement and tree-planting techniques that help absorb instead of repel water.

“In addition to routine water quality sampling, the Department monitors rainfall levels that can compromise beach water quality which may trigger beach advisories,” a representative from the city’s Department of Health and Mental Hygiene said in a statement.

The department lists the current beach advisories on its Web site, nyc.gov/health.