In late November, a fishing operation pulled 10,244 carp from Cherokee Marsh.
Dane County Clerk Scott McDonell wishes they'd killed more. "The only good carp is a dead carp," he jokes. "They're not a native species. And the effects are pretty dramatic."
McDonell made cleaning up the lakes a priority when he was chair of the Dane County Board and has continued to do so since becoming clerk.
Over the past century, Cherokee Marsh has become more of a lake, as the marsh area erodes and recedes. Restoring it is one of the ways officials are fighting pollution in the Yahara lakes. Healthy marshland keeps farm runoff from polluting the lakes.
The common carp, which was introduced to the area by European settlers in the 1880s, is blamed for about 25% of the marsh's destruction. As bottom feeders, the fish also dig up nutrients on the bottom of the lake, muddying the water and disrupting its chemical balance.
"That bottom sediment is where the phosphorus resides," says Kurt Welke, a fisheries biologist with the state Department of Natural Resources. "The carp make that phosphorus available."
Carp are edible, and some people love them. But in general, most anglers (and eaters) prefer native fish, like perch, pike, bass and walleye. Carp are oily and bony. Welke compares them to pomegranates: "I like pomegranates, but you've got to work at them" to enjoy the edible parts.
The carp spawn prodigiously and grow quickly. They can reach 10 to 11 inches -- outgrowing any predator -- in about six months, Welke says. And they can live for decades. One fish pulled out of Lake Wingra was estimated to be 59 years old.
"They escape the vulnerability stage very quickly," Welke says. "Which explains why they have done so well in North America. They're found almost everywhere. And where they're found, they're in nuisance numbers."
The November harvest killed about 10% of the carp population in Cherokee, which is estimated at 90,000. The fish are easiest to catch during the winter months, when they congregate in one area and can be scooped out.
Of the 10,000 fish pulled from Cherokee, about half were sent to ethnic markets in big cities, the other half to factories, where they were turned into pet or human food.
It's unlikely that the county will eradicate the carp. But reducing the population by about 40% could have dramatic effects on the water quality of the Yahara Lakes, Welke says.
In 2008, a similar fish harvest in Lake Wingra had an immediate effect on clearing the water. But that allowed sunlight to reach the bottom, spurring plant growth, Welke says. "Now Lake Wingra is a very weed-dense, some would say a weed-choked, lake," he says. "Now the question is, did we win?"
In the case of Cherokee Marsh, spurring plant growth is exactly the goal.
McDonell notes that the carp kill is just one part of an effort to restore the marsh. And improvements there benefit the lakes downstream, including Mendota and Monona.
"I'd like to get back to the days when kids swam on the beach of our lakes," McDonell says. "They didn't go to Goodman pool, they swam in the lakes. And I think we should get back to that."
