During routine water quality tests, staff found a high level of enterococcus bacteria.
Sarasota County health officials have issued a no swim advisory for Siesta Key beach because of bacteria in the water.
During routine testing, staff found concentration of enterococcus bacteria outside of normal limits. Enterococcus bacteria comes from a variety of natural and human-made sources including pet waste, birds, stormwater runoff and human sewage from failed septic systems, though no sewage spills have been reported within one mile of the beach in the past two weeks.
The Sarasota County rapid response team determined the cause of the bacteria is likely due to natural sources, such as wrack lines and recent landfill, which have attracted pollutants into the area.
The beach remains open, though swimming and other water recreation is not recommended, because it could make people ill, Department of Health in Sarasota administrator Tom Higginbotham said.
"People, especially those who are very young, elderly or who have a weak immune system, who swallow water while swimming can get stomach or intestinal illnesses," he said. "If water comes in contact with a cut or sore, people can get infections or rashes."
Signs advising the public against entering the water will stay in place until follow-up water testing results meet the Environmental Protection Agency's recreational water quality standard.
Residents also should not eat shellfish collected in the immediate area of the beach until the advisory is lifted. Finfish caught live and healthy can be eaten if filleted.
To help keep beach water safe for swimming and recreation, residents are asked to keep pets from roaming on beaches and in park areas, and to pick up pet waste. Additionally, children in diapers and people of all ages with diarrhea should refrain from going in the water.
The Florida Department of Health in Sarasota County expects to have new test results available after 2 p.m. Friday.