The Lake Where You Live

I grew up in a small town on Lake Michigan and saw firsthand the proliferation of zebra mussels there. They encrusted hard surfaces and clogged water utility intake pipes. Their shells built up in windrows on the beaches.

Then in 2000, along came quagga mussels, even more problematic because unlike the zebras they don’t need a hard substrate to cling to — in places, they carpeted the lake’s sand bottom. Both species came into the Great Lakes system in the ballast water of ocean-going freighters. 

Zebra mussels have taken hold in a number of inland lakes in Minnesota and northwestern Wisconsin, where besides creating a nuisance for property owners they’ve significantly changed the ecosystems and fisheries.

Then last July, quagga mussels were discovered in Lake Geneva in southeastern Wisconsin’s Walworth County. They were found by interns with the Geneva Lake Environmental Agency who were doing routine research. It was the first discovery of this mussel species in a Wisconsin inland lake.

How problematic can these mussels be? In 2000, zebras made up 98 percent of Lake Michigan’s mussel population. Five years later, quagga mussels had taken over. Now they cover much of the lake bed, in some areas in numbers up to 7,900 per square meter.

Jake Vander Zanden, director of the UW-Madison Center for Limnology, told Wisconsin Public Radio last year that quaggas would be better adapted than zebras to colonize our state’s inland lakes because of the largely soft lake bottoms. In addition, they thrive in colder and deeper waters than zebras can tolerate. 

Zebra mussels were already present in Lake Geneva when the quaggas were discovered. The quaggas are somewhat bigger than the dime-sized zebras. In addition, their shells are curved on all sides, while zebras’ shells have one flat side. 

Both species are filter feeders: They take in water and strain out particles, including the tiny algae cells that form the base of the lake food web. When abundant, their feeding makes the water extremely clear, but that doesn’t mean the lake is healthy. It means the mussels have captured the nutrient base, leaving less food for larval fish and aquatic insects. 

The excrement from zebra and quagga mussels is high in nitrogen, which can feed a noxious bottom-dwelling algae called Cladophora, which then can die, release foul odors, and foster growth of bacteria that cause botulism, harmful or lethal to fish and waterfowl. 

Not all lakes are susceptible to explosions of these mussels: both species require enough calcium in the water to form their shells. 

The two mussel species are spread mainly by recreational boats transported from lake to lake. That is most likely how quagga mussels got into Lake Geneva, and it is the most probable pathway for either species into our northern lakes. Their larval forms, called veligers, are very small and can easily hitch rides in boat bilges, bait pails, live wells, outboard motors, and the ballast tanks of wakesurf boats.

This is another reason why boat hygiene and landing inspections under Clean Boats Clean Waters are increasingly essential. 

I invite you to attend my presentation at the Minocqua Public Library at 5:30 p.m. on Thursday, May 22. 

Ted Rulseh, a writer, author and advocate for lake protection, lives on Birch Lake in Oneida County. Visit him and his blog at https://thelakeguy.net.