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UW-Madison students find zebra mussels in Lake Mendota

October 21, 2015 By Adam Hinterthuer

Photo: Zebra mussels in a jar

Samples collected in Lake Mendota near Hasler Lab. Photo: Adam Hintertheur

An undergraduate class at the University of Wisconsin–Madison has discovered another invasive species in Lake Mendota.

Students in Zoology 315, a popular limnology course taught by UW–Madison Center for Limnology (CFL) Professor Jake Vander Zanden, found the hard-shelled animals while participating in a laboratory session this October.

Zebra mussels are considered filter feeders. They suck in water, filter out what’s edible and then “spit” out the rest. They have been known to inhabit several nearby lakes, including Lake Wisconsin and Lake Ripley, and have also invaded the Great Lakes.

While the animals can cause dramatic increases in water clarity, they can also disturb lake ecosystems, throwing off the balance that allows other species to thrive. For example, carp often do well in lakes invaded by the mussel, while walleye can struggle. Zebra mussels can also cause large, odorous mats of algae to break off of the bottom of lakes and decompose onshore.

Photo: Zebra mussel in a brick

Most of the zebra mussels Vander Zanden and his students are finding in Lake Mendota are tucked into crevasses, like the specimen seen in this piece of brick.

Photo: Chelsey Blanke

The mussels can also attach to the hulls of boats, clog water intakes found along the lake, and coat the bottoms of lakes with sharp shells that present a hazard to watergoers.

Vander Zanden and a number of CFL graduate students are now actively surveying the lake to better understand the distribution and abundance of these invasive species. Their numbers are, for now, low, but the researchers will continue to monitor the lake to better understand what impact they may have on Lake Mendota. The scientists are also working with the Wisconsin Department of Natural Resources to manage these invaders.

It’s unclear how the mussels made it into Madison’s largest lake, but the animals can be transported on boats and their microscopic larvae can be carried from one body of water to another in bait buckets. The finding underscores the importance of practices that prevent the spread of invasive species, like cleaning gear between lake trips, checking for invasives growing on boat hulls and wheel wells of trailers, and never mixing water sources.

For more about the students and their find, visit