The swim beach at Chatfield State Park in Jefferson and Douglas counties was shut down Tuesday morning after a test discovered elevated levels of E. coli bacteria in the water.

The closure was announced by Colorado Parks and Wildlife just before 11 a.m. Agency officials said they administered additional testing and expect results in the next 24 hours.

On Tuesday, the water’s E. coli concentration tested above 235 organisms per 100 milliliters, requiring the closure under state guidelines.

The water’s E. coli levels will have to test in normal ranges before the swim beach can reopen.

The Colorado Department of Public Health and Environment mandates natural swim areas be tested for E. coli weekly. In the week before the most recent test, the swim beach’s results came back normal, according to the agency.

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E. coli is a naturally occurring and very diverse bacteria. While most strains of E. coli are harmless, some can cause illnesses, including diarrhea, urinary tract infections, respiratory illness and pneumonia, according to the Centers for Disease Control and Prevention.

The bacteria is often transmitted to humans through the consumption of contaminated foods that are raw or undercooked, or by consuming contaminated water.

Elevated E. coli levels can be caused by fecal waste in the water from humans or animals, malfunctioning septic systems and excessive runoff from rain and floods or from urban, suburban or rural areas, according to Colorado Parks and Wildlife.

The temporary closure only affects the swim beach. The rest of Chatfield State Park will remain open as usual.