Norovirus is a stomach bug that causes vomiting and diarrhea. It can be contracted through contaminated water, including dirty lakes and pools, the CDC warns. Creative Commons

The stomach bug norovirus has become infamous for sickening hundreds of passengers on cruise ships. But it's also possible to catch the virus, which causes vomiting, diarrhea and nausea, while swimming, say, in your local lake, river or town pool, according to a report released Thursday by the U.S. Centers for Disease Control and Prevention.

The center's report highlighted an outbreak of norovirus that sickened 70 people in Oregon in July 2014, which it linked to a contaminated lake that people had been using for recreation, including swimming. Those who swam in the lake were 2.3 times more likely to get sick than those who did not go in the water, the CDC found.

Norovirus is highly contagious and can be passed from one person to another through contaminated foods or surfaces, notes the CDC. Far beyond its penchant for striking cruise ship passengers, the virus is fairly common and accounts for 19 million to 21 million cases of sickness in the U.S. every year.

But how did so many visitors who went swimming at Blue Lake Regional Park in Oregon last summer get sick? Experts theorized that a swimmer who had been sick with norovirus vomited or had diarrhea in the lake, contaminating water that others then swallowed.

"Keeping germs out of the water in the first place is key to keeping everyone healthy and helping to keep the places we swim open all summer," said Michael Beach, associate director for healthy water at the CDC.

After the outbreak in Oregon last July, the lake was closed for 10 days. Most of those who were sickened were children aged 4 to 10 years. Swimming areas that are not treated with chlorine, such as lakes and ponds, are riskier than those that are, such as pools that have been properly maintained.

As spring heats up into summer and the swimming season begins, the CDC recommends that people avoid swimming if they had been sick and that children be taken on bathroom breaks to prevent accidents in the water. It also suggested swimmers avoid swallowing water from lakes and pools.