Norovirus Named in Washington Lake Outbreak

— -- The stomach bug that sickened more than 260 swimmers at a Washington state lake was in fact norovirus, health officials have confirmed.

The contagious virus swept through Horseshoe Lake Park in Kitsap County, Washington, earlier this month, causing cramps, nausea and diarrhea, according to the local health department.

The park was closed as officials investigated the cause of the outbreak, which was initially dubbed “norovirus-like.” It reopened Saturday after water samples from the lake came back negative for the virus.

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The same virus sickened more than 100 people at Idaho’s Eagle Island State Park last week, according to the local health department.

Norovirus is the sixth-leading cause of recreational water illness in the U.S., according to the Centers for Disease Control and Prevention –- tying with the bacteria E. coli. Each year the virus causes more than 19 million cases of illness, 400,000 emergency room visits, 71,000 hospitalizations and 800 deaths, according to the CDC’s website.

The virus spreads through food, liquid and surfaces that are contaminated with infected feces or vomit, according to the CDC. There’s no specific treatment, so the agency recommends staying hydrated for the duration of symptoms, which is usually one to three days.

The CDC recommends the following tips for safe summer swimming:

• Avoid getting water up your nose when swimming in warm, freshwater.
• Keep poop, pee and germs out of the water.
• Don't swim if you have diarrhea.
• Shower with soap before taking a dip.
• Wash your hands after using the toilet or changing diapers.
• Check the free chlorine level and pH before getting into the water (click here for the recommended levels)
• Don't swallow the water.

ABC's Dr. Richard Besser contributed to this story.