From 2005 through 2009, Hudson Beach closed 2 times (10 days total) for blue green algae levels, 3 times (18 days total) for high bacteria levels, and 5 times (42 days total) due to high levels of both. In addition, all Lake Monona beaches were closed for a week in 2008 due to a raw sewage release from an MMSD pumping station.
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More information is available on the Public Health, Madison & Dane County website