John McLaughlin
A view of the Capitol from the snow-covered shore of Lake Mendota at Governor’s Island.
Just as you’ve been clearing out your gutters and putting a cover over the air-conditioning unit, Dane County has been preparing the lakes for winter.
To prevent shoreline ice damage and to allow for flood storage capacity after spring runoff, water levels are being drawn down in the Yahara River chain of lakes: Mendota, Monona, Waubesa and Kegonsa. (Lake Wingra is connected to Monona but is not considered part of the chain.)
The state Department of Natural Resources governs our lake levels. During summer months, the county keeps them within a certain range. “Each lake has a different elevation, but in terms of the range it’s six inches,” says John Reimer, county stormwater engineer. Reimer says the county plans to “operate to the mid-range,” keeping fluctuations to within three inches.
The county also operates the 10 weed-harvesting vessels often seen near shore. A “weed scout” precedes them, observing and forecasting potential problems. Besides presenting aesthetic concerns, weeds can be a nuisance to navigation, but that’s not the main reason for their removal.
“We remove lake weeds to make sure flow is maintained in the rivers, so if we ever do get flooding, the rivers aren’t choked off by vegetation,” says Reimer. “We try to be proactive about that.”
The Tenney locks closed Oct. 31, and Dane County has already removed more than 160 buoys in the Yahara chain. “If people are using the lakes, be aware of any hazards that would be out there,” warns Reimer. With lower lake levels “some of the hazards out there can become more exposed.”
Lake prep got a bit more complicated with the recent discovery of zebra mussels in Lake Mendota. The county is asking anyone who will be removing piers, docks and boats from the water to check for attached zebra mussels.
A class of University of Wisconsin-Madison undergraduates found the mussels in October. The good news is that an Oct. 22 survey suggests the damaging invasive species is not in Lake Monona — yet. Their absence in that lake is one of several mysteries surrounding the discovery.
“They’re at Picnic Point, Maple Bluff, Tenney Park, University Bay, Frautschi Point — they are widespread,” says professor Jake Vander Zanden of the UW Center for Limnology. Zebra mussels can encrust piers, boats and motors and clog water intakes and pipes, and their shells can cut swimmers’ feet.
Vander Zanden estimates that they’ve been in Mendota for three years, but so far they’re hard to find — something like one per square meter.
“Typically when we see zebra mussels in an invaded lake, we see thousands or even hundreds of thousands per square meter,” he says. “When they’re at those really high abundances, they have huge impacts. We may have captured it really early on in the invasion process.”
Zanden says it’s “sort of remarkable that they’ve only just appeared.” he says. Zebra mussels have been spreading in southern Wisconsin since the 1990s. At the moment they’re hiding in Mendota’s nooks and crannies, not on rock surfaces.
“That could suggest that fish are feeding on baby zebra mussels,” says Vander Zanden. “I think there could be some ecological sources that are holding them back. Do I have evidence of that? No.”
Colin Smith, a graduate student at the Center for Limnology, led the Oct. 22 scuba search of six sites in Lake Monona.
Smith was surprised the search turned up no zebra mussels. “For me, these results generated more questions than relief,” he says. “Why did we not find them at the survey sites? Would we have found them at other sites in the lake? Are they located deeper in the lake? Is Monona not suitable for their establishment? What’s next?”
Vander Zanden warns that other invasives may be on the way, including quagga mussels, red swamp crawfish and bloody red shrimp.
As for zebra mussels? “I really don’t think there’s anything we can do, other than see what we can learn,” he says.
If you find zebra mussels in lakes other than Mendota, the DNR would like to hear about it. If possible, note the location and take a digital photo of the animal and its setting; collect up to five specimens of varying sizes; place in a jar with water; put on ice and transport to a refrigerator. Then contact Susan Graham at the DNR, susan.graham@wisconsin.gov.
