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Nuisance Algae (Cladophora) in Lake Michigan

For the past few years, large quantities of decaying algae, called Cladophora, have been found along Wisconsin's Lake Michigan shoreline. As the algae and organisms trapped in the algae rot, they generate a pungent septic odor that many people confuse with sewage. Nutrient sources like phosphorus and nitrogen, zebra mussels and declining lake levels have been implicated in the recent increase in nuisance algae.

The presence of rotting Cladophora on Lake Michigan beaches presents aesthetic and odor problems that impair recreational uses of the lake. Cladophora itself does not present a risk to human health. However, Cladophora rotting on a beach promotes bacterial growth that can pose a risk to human health. In addition, crustaceans that wash up with the algae can attract large flocks of gulls, resulting in high concentrations of fecal material and bacteria.

Cladophora – Natural Green Algae

Cladophora is a green algae found naturally along the Great Lakes coastlines. It does not produce toxins the way blue-green algae can. It grows on submerged rocks, logs or other hard surfaces. Because of Lake Michigan's excellent water clarity, it has been observed growing underwater at depths of more than 30 feet. Wind and wave action cause the algae to break free from the lake bottom and wash up on shore.

Nuisance levels of Cladophora were also a problem in the Great Lakes in the 1960s and 70s. Research linked these blooms to high phosphorus levels in the water, mainly as a result of pollution from lawn fertilizers, poorly maintained or inadequate septic and sewage treatment systems, agricultural runoff and urban runoff that contained phosphorus from detergents. Due to tighter restrictions, phosphorus levels declined during the late 1970s and Cladophora blooms were largely absent in the 1980s and 90s.

Phosphorus levels in Lake Michigan continue to remain below the thresholds set in the 1970s, but recent research suggests that the invasion of zebra and quagga mussels in the Great Lakes are responsible for the increase in algae. These invasive species activities increase the availability of phosphorus for Cladophora and increase water clarity. Since it is difficult to adequately control zebra mussel populations, the best management option is to reduce phosphorus entering Lake Michigan.


These videos, produced by Wisconsin Sea Grant, provide a good introduction to Cladophora along Lake Michigan.

Additional Resources