About 12,000 gallons from an underground sewage tank flooded into Lake Washington Wednesday.

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A large underground sewage storage tank spilled about 12,000 gallons of sewage into Lake Washington Wednesday morning, prompting the beach at Seward Park to close, according to a Seattle Public Utilities news release.

Water samples off the beach are being tested for possible fecal coliform, said utilities spokesman Andy Ryan.

If any fecal coliform is found, Ryan said “that’s bad to swim in because it can make you sick.”

E. coli is a species of fecal coliform, according to the Environmental Protection Agency. The agency says it  recommends “E. coli as the best indicator of health risk from water contact in recreational waters.”

The test results come back Thursday, meaning the beach is closed at least until then.