The water in the local swimming pool and water park may look clean and clear, but those pristine-looking fun spots are where most people catch bugs associated with summertime parasites. Public health officials say 40 states, including California, and Puerto Rico have seen an uptick in cryptosporidium, or crypto, which can cause weeks-long bouts with diarrhea.

In raw terms, new data from the federal Centers for Disease Control and Prevention shows a strong likelihood that people are spreading the disease, which can cause "profuse, watery diarrhea" for up to three weeks, by jumping into the water too soon after they've been sick. In our state, between 1 and 4 cases of crypto were reported at public pools during the period from 2009-2017.

When the poop of humans and animals infected with the parasite gets in the water — even chlorinated water, where it can survive for up to seven day — others can become sick if they swallow the contaminated water, the CDC said. The CDC said 35 percent of outbreaks of cryptosporidiosis were linked to treated swimming pools and water playgrounds from 2009 to 2017, the latest year for which data are available. Crypto outbreaks increased annually at an average rate of 13 percent, and nearly 7,500 people were sickened in 444 Crypto outbreaks. Although cryptosporidiosis is almost never fatal, one person died during the period and 287 others required hospitalization.

The report released Friday also showed that during the period of 2009-2017: More than a third of the 444 cases of crypto — 156 — were in swimming pools, kiddie pools and water playgrounds;

Twenty-two cases originated from untreated water, such as lakes;

Eight-six cases involved contact with animals, mostly cattle;

Fifty-seven cases were associated with child-care settings;

Twenty-two cases were food-borne, most involving unpasteurized milk or apple cider;

Most cases were reported in the months of July and August, and 2016 was the peak year for outbreaks, with more than 80. CDC graphic Crypto is a challenging parasite to control because it has a protective outer shell that makes it difficult to kill. And not only can it survive for days in chlorinated pools and water playgrounds or on surfaces disinfected with chlorine bleach, it only takes a few germs to make someone sick. "There can be millions of crypto germs in poop," the CDC said. "Someone sick with crypto can have diarrhea for up to three weeks."

The agency recommends that people not swim for at least two weeks after their last bout with diarrhea.

That's important because nearly a quarter of Americans say they would jump into a swimming pool within 24 hours of a bout with diarrhea, according to a survey released last month by the Water Quality & Health Council. That report also found 51 percent of Americans report using a swimming pool as a communal bathtub, either using swimming a substitute for showering or using it to rinse off after strenuous work.

The public at large has a responsibility to control the spread of crypto, the CDC said. "Young children can get seriously sick and easily spread crypto," Michele Hlavsa, a registered nurse who heads the agency's Healthy Swimming Program, said in a statement. "They don't know how to use the toilet and wash their hands, or are just learning how. But we as parents can take steps to help keep our kids healthy in the water, around animals, and in childcare."