The Quarry Lakes Regional Recreational Area in Fremont is closed for swimming through at least Wednesday, according to the East Bay Regional Park District.
Other parts of the park will be open, park officials said.
Park officials said they are prohibiting swimming because of a toxic blue-green algae bloom that can cause visitors skin irritations and other symptoms.
Officials said toxic blue-green algae blooms are rare and this one was most likely caused by the drought. Officials said they will have water-quality tests done before allowing visitors to swim again.