As was the case on Mink and Somers, most rotenone treatments are on shallow and highly fertile waters, called eutrophic lakes. Removing the rough fish allows sediments to settle and sunlight to reach the aquatic vegetation. Despite its success improving Mink and Somers and dozens of other lakes, rehabilitation is controversial. Native-fish fans contend that the kills reduce a lake's biological diversity. And some residents near lakes scheduled for treatment protest the rotenone applications out of health concerns.
DNR biologists defend the treatments as prudent, safe, and expedient.
But we're aware of concerns, and we work to clear up common misconceptions about lake rehabs. Killing and removing the roughfish is only one step in restoring degraded shallow lakes, says Peterson. Just as important but far more difficult is finding ways to reduce the amount of farmland and residential runoff polluting the water. At Sleepy Eye Lake, south of New Ulm, nutrients and other contaminated runoff flow in from distant farm fields and nearby parking lots, streets, and lawns. The nutrients fuel algae blooms, which deplete the shallow, 200-acre lake of oxygen needed by game fish.