On the cusp of the unofficial start of summer, the Centers for Disease Control warns that recreational water illnesses are on the rise. The CDC says there were more recreational water illnesses outbreaks in 2007 than ever before, and the numbers could increase in the coming years.

Government agencies are hopelessly addicted to acronyms and therefore refer to recreational water illnesses as "RWIs" -- illnesses that are spread by swallowing, breathing, or having contact with germs in the water of swimming pools, spas, lakes, rivers, or oceans.

"The leading cause of RWI outbreaks is Cryptosporidium or Crypto, a chlorine-resistant parasite, primarily associated with treated swimming places, such as pools and water parks," according to Michele Hlavsa, an epidemiologist at the CDC.

"This RWI has been a public health issue in the past and will likely pose an even bigger challenge in the future."

During 2004-2007, the number of Crypto cases tripled. At the same time, the number of Crypto outbreaks linked to swimming pools more than doubled. Because Crypto is chlorine resistant, even a well-maintained pool can transmit this parasite.

"People need to practice healthy swimming habits, such as not swimming when they have diarrhea, not swallowing the water, taking a shower before swimming, washing their hands after using the toilet or changing diapers, and washing their children thoroughly -- especially their bottoms -- with soap and water before swimming. To prevent outbreaks, we encourage pool operators to add supplemental disinfection to conventional chlorination and filtration methods," said Hlavsa.

Symptoms generally begin two to 10 days after becoming infected with the parasite.

Crypto is characterized by watery diarrhea lasting one to three weeks. It can be spread by swallowing recreational water contaminated with Crypto or by putting something in your mouth or accidentally swallowing something that has come in contact with the stool of a person or infected animal.

Other symptoms include stomach cramps or pain, dehydration, nausea, vomiting, fever, and weight loss. Crypto is not spread by contact with blood.

Some people with Crypto will have no symptoms at all, and most people who have healthy immune systems will recover without treatment. People with weakened immune systems are at risk for severe or life-threatening illness.