A pesky summer visitor has shown up on Wisconsin’s Lake Michigan shorelines the past six years. It’s Cladophora, an algae that drives off beachgoers with a pungent, stinky stench as it decays in massive heaps along the shore. Victoria Harris, UW Sea Grant’s water quality specialist, has been working with colleagues around the state to gather information about the algae’s resurgence in nearshore waters and answer questions from the public.
Harris says rotting Cladophora can exacerbate beach closings because it often harbors large numbers of Escherichia coli bacteria. Gulls like to eat the zebra mussels and other fauna snared by the algal mats, and gull fecal matter is loaded with the bacteria. Though no definitive cause has been identified, she says a myriad of interconnected conditions appear to be involved—a combination of low lake levels, increased light penetration of the water, a rise in available nutrients, favorable water temperatures and the form of shoreline substrate.
Zebra mussels, which invaded Lake Michigan around 1991, may be largely to blame by affecting water clarity and recirculating nutrients. Following the research meeting, Harris helped organize and present her findings at a public forum with Wisconsin DNR staff to inform homeowners, beach managers and other concerned citizens about the algae. Presently, she said, removing the algal mats from beaches and trying to control phosphorus inputs to the nearshore are the best way to handle the outbreaks. For more information, download a factsheet.