A new website reveals how often and how badly Long Island Sound beaches are contaminated with bacteria, and even zooms in on possible causes.
While rainfall can shut beaches as overloaded sewer systems release sanitary waste, the riskiest beaches might be ones that must be closed even in dry weather, said Tracy Brown, director of the western Long Island Sound programs for Save the Sound.
The not-for-profit's new online tool, Sound Health Explorer, shows beaches also can be contaminated during sunny periods if they are near failing cesspools and septic systems, leaking sewer pipes or sewers illegally connected to waste systems.
The site is at soundhealthexplorer.org.
"The key is to know which beaches you should avoid just after a rainfall and which ones you have to avoid rain or shine," Brown said.
Town officials might pre-emptively close a beach after a rain, but during a sunny week might not discover bacteria until the next test.
"The chances are the beach was open and people were probably swimming, and you don't know until the next day that that beach was polluted," Brown said.
On average, beaches are tested once a week, though some schedules differ, she said. The website, using data from 2004 to 2014, shows how often and when each beach is tested, she said.
It will be updated when new data are issued by the U.S. Environmental Protection Agency and many other sources, Brown said.
While no Suffolk beaches got failing grades last year, Oyster Bay's Beekman Beach in Nassau got a D-plus.
However, nearby Theodore Roosevelt Beach "is among the most reliably clean," the group said, showing how localized this problem can be. Oyster Bay officials had no immediate comment.
Suffolk had 27 A-plus beaches last year, Brown said, while Nassau had one: Bayville's Creek Beach.
If sufficiently concentrated, this contamination can cause viral, parasitic, and bacterial infections in swimmers.
State Assemb. Steve Englebright (D-Setauket), a geologist, said the tool makes it easy to compare the safety of different beaches.
"They are bringing good citizen science and participation into the realm of policy," he said.
Unlike nitrogen pollution, now a severe and constant problem on Long Island, bacteria from human waste are shortlived, thanks to the sun and waves, experts said.
Suffolk's beaches outperformed Nassau partly because water in the Sound circulates much more freely in the east than in Nassau, because it has so many more harbors, noted Christopher J. Gobler, a professor with Stony Brook University's School of Marine and Atmospheric Sciences.
Also, while Nassau is far more developed and has many more sewer lines than Suffolk, this advantage is partly undercut because some systems mix with stormwater, experts said.
Brown said she hoped the data will prompt residents to require their towns to ensure their beaches are safe.
Swimmers also might wish to avoid algae blooms, experts said, though only the blue-green variety, which again has bloomed in Lake Ronkonkoma, directly causes illnesses and prohibits swimming.
Richard Amper, executive director of the Pine Barrens Society, pointed out that Long Islanders also can track several measures of water quality, including algae blooms, by signing up for weekly reports from the Long Island Clean Water Partnership, an umbrella group.