With the March 20 declaration of open water after almost three months of ice, Madison’s five lakes are again becoming home to a variety of watersports, including swimming, kayaking, fishing and more. The defrosting of the lakes also provides a space for the formation of algal blooms each year.
Cyanobacteria blooms, also known as blue-green algae blooms, develop in late spring and early summer when the three conditions needed for their formation — heat, nutrient runoff and direct sunlight — are met. Cyanobacteria can produce toxins that are harmful to people, especially children, and pets if they are absorbed through the skin, inhaled or swallowed.
The algal blooms, according to Public Health Madison & Dane County, appear blue-green, reddish-purple or brown and tend to float. The city recommends that people do not swim in water with apparent algae and not to boat over such water, as people can be exposed to toxins through inhalation.
“The things that dissipate it are wind — it can’t form on choppy water — and the same problem that causes it also helps get rid of it,” explained Adam Sodersten, the Marketing and Communications Director for the Clean Lakes Alliance, to Wisconsin Public Radio (WPR) last year. “If you get rain that will also bust it up … there’s no real timeframe, unfortunately.”
In 2020, Lake Mendota and Lake Waubesa saw blooms as early as June 3, according to WPR. Public Health Madison & Dane County tests the water at various beaches for E. coli and blue-green algae from Memorial Day until Labor Day.
The lakes closest to the heart of Madison – Monona, Mendota and Wingra — tend to receive excess phosphorus runoff from construction erosion and leaf management. The more rural of Madison’s lakes — Waubesa and Kegonsa — get their overabundance of nutrients from agricultural cropping practices.
To improve water quality in all five lakes connected through the Yahara River, the Clean Lakes Alliance has developed the Yahara CLEAN Compact, which is a plan meant to “improve the condition and usability of our lakes and beaches.” The plan, released in 2012, highlights the need to reduce phosphorus and outlines over 70 recommendations to improve water quality in all five Yahara lakes.
The presence of algal blooms does not mean that water recreation is impossible this summer, but the safest thing to do if you plan on swimming, boating or fishing is to wait for the algal blooms to clear. Water conditions are updated on the Public Health Madison & Dane County website.
state news writer