OSCEOLA, Mo. –The chance of a swimmer in the U.S. being attacked by a shark is close to zero. But dangerous creatures do lurk in our waters, including lakes, ponds and even concrete swimming pools.

Microbes such as cryptosporidium, shigella, giardia and E. coli frequently live in public swimming areas. All three cause diarrhea if ingested.

“Accidently swallowing contaminated water, or even getting it in your mouth, can make you ill,” said Saralee Bury Jamieson, human development specialist for University of Missouri Extension. “You can also get infections in eyes, ears and nose, as well as in cuts and scrapes.” Public health professionals call swimming-related sicknesses “recreational water illness.”

There’s an even greater risk for people with compromised immune systems.

“Children, pregnant women and the elderly are more at risk of becoming seriously ill if they are infected,” Jamieson said.

According to the U.S. Centers for Disease Control and Prevention, cryptosporidium, or crypto, can survive for days, even in chlorinated, well-maintained pools.

CDC statistics show that crypto is the leading cause of swimming pool-related diarrhea, with crypto cases jumping from 3,400 in 2004 to more than 10,000 in 2008.

However, there are simple steps you can take to stay safe. Never swallow swimming water, and try to avoid getting the water in your mouth. If you’re ill, be considerate and stay out of the water, Jamieson said.

“Don’t swim when you have diarrhea. You can spread germs and make other people sick.” she said.

Swimming hygiene can help keep you and others safe.

“Before entering a swimming pool, shower with soap and water, and wash your hands with soap and water after using the bathroom, after swimming, and before eating,” Jamieson said. “Never change a diaper at poolside, and wash your hands after changing a diaper.”

Also, take children on frequent bathroom breaks to avoid accidents in the pool, she said.

Runoff after a rainfall will increase the amount of microbes in the water. “Do not swim in lakes and rivers after it rains or if the water is cloudy,” Jamieson said. “Wastewater runoff is highest following a rain.”

If you are not certain about the condition of the swimming area, keep your head and face out of the water, Jamieson said.

For more information on healthy swimming, contact your local health department or visit www.cdc.gov/healthywater/swimming.