It’s still very early in the season, but at least five swimming areas have been closed by algae blooms in Madison. A spokesperson for the Clean Lakes Alliance blames excessive heat, calm winds and a lot of run-off for the growth of a substantial blue-green algae bloom. The phosphorus gets into the lake water and isn’t dissipated, causing the problems. Blue-green algae is toxic to both animals and people. Swimming areas at Memorial Union Pier, Olin Park, Spring Harbor, Lake Mendota County Park and Marshall Park are currently closed to swimmers. The water is tested at Dane County beaches every week.