A mysterious intestinal ailment that struck down about 200 people who swam in a Washington lake has pushed officials to shut down access to the lake.

The swimmers who enjoyed a summer weekend at Horseshoe Lake have been reporting symptoms of nausea, cramps and diarrhea, officials said.

The officials suspect a norovirus may be the culprit but are awaiting test results.

In the meantime the popular Horseshoe Lake County Park swimming site has been closed to vacationers until further notice, they say, and warning signs have been posted on the lake shoreline.

"Although there is no laboratory confirmation of a specific virus or bacteria responsible for the illnesses at this time, Public Health and Kitsap County are issuing the temporary closure as a precautionary measure while they investigate and to protect the public and prevent any additional illnesses," the county public health district said [pdf] in a statement.

The county park is apparently the only area on the lake affected so far, officials said.

Norovirus is a contagious strain known to cause widespread illnesses.

The virus was blamed for two recent incidents of illness among cruise ship passengers, on Princess Cruise's Crown Princess in April and Royal Caribbean's Explorer of the Seas in February.

It can spread in food, liquids or by contact with surfaces contaminated with infected vomit or feces, as per the U.S. Centers for Disease Control and Prevention.

There are no specific treatments for norovirus, said the CDC, which recommended people stay well hydrated if they began showing symptoms.

Kitsap health officials urged people affected by the symptoms to visit a doctor if the symptoms were severe or did not improve within 24 hours.

Symptoms should improve within a day or two on their onset in most cases, they said.

Those experiencing diarrhea illnesses should conduct frequent and diligent hand-washing using soap and warm water to prevent any spread of infection to others.

Additional water samples for laboratory testing were being collected, and restrooms at the park were being thoroughly cleaned during the announced closure.

The park closing was met with disappointment by some locals.

"It's a bit of a bummer for [the kids]," said Doug Chase, vice president of Crista Camp. "They'd love to be out on the water [with] toys and having a blast, but we feel like the conservative approach is best."