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A massive blue-green algae bloom has forced the closure of several Madison-area beaches including a stretch of Lake Mendota from UW-Madison to Middleton.

Beaches and piers at Memorial Union, Marshall Park, Lake Mendota County Park and Spring Harbor on Lake Mendota are all closed, as is the beach at Olin Park on Lake Monona, Public Health Madison and Dane County announced late Thursday afternoon.

People and pets are advised to stay out of the water during blooms of blue-green algae, or cyanobacteria, which can release harmful toxins, according to the Clean Lakes Alliance.

The toxins can cause issues such as upset stomach, rashes and respiratory problems. Such blooms can also lead to fish kills once the bacteria sinks, according the UW Center for Limnology.

Earlier Thursday, Public Health noted that all area beaches were open but cautioned beachgoers to beware of water conditions whenever they approach a beach. Shortly afterward, reports came in of several blue-green algae blooms along the shoreline and even near the lake’s center.

“We are at the beaches taking water samples weekly,” operations supervisor Sarah Mattes said, adding that the department also depends on citizen reports and organizations like the Clean Lakes Alliance to get a real-time understanding of the lakes’ conditions.

Until the bloom passes, people planning on outdoor activities around the lake should refrain from getting in the water. The condition of the lake should not take too long to get better, according to the UW Center for Limnology.

For the latest beach closings, go to: go.madison.com/beach-closings.