Last week, the Minnesota Department of Natural Resources went ahead with its plan to poison two lakes near Forest Lake, Minn., in an attempt to rid them of unwanted rough fish, including carp and bullhead, to make way for game fish, like northern pike to take over.
The department used a mixture containing rotenone, a common garden pesticide and potent fish toxin, to kill the fish. The department said this strategy is effective against shallow lake invaders that stir up the lake bottom, making the water cloudy and limiting grasses that waterfowl use for food. The department, Ducks Unlimited and the Minnesota Waterfowl Association all say ducks and geese will become more abundant at the lakes by next year.
Rotenone has been used in Minnesota lakes since 1945 without much controversy, but the chemical does have disadvantages. It has been experimentally linked with diseases similar to Parkinson’s in high doses, although it is not proven as a carcinogen. Low doses seem to be relatively harmless, if those involved take the proper safety precautions.
Rotenone’s most detrimental effects appear to be on biodiversity. As a pesticide, it eliminates a large percentage of a lake’s aquatic insects, although it seems these populations are generally able to bounce back within a couple of years. If used indiscriminately, it can allow non-native fish to take over a lake and actually eliminate threatened native species. However, strict permits are required for its use in poisoning plans, and if done correctly, it can help restore ecosystems such as Howard and Mud lakes in Minnesota, which had been taken over by invaders.
Some environmentalists argue that the department should have pursued other approaches, such as reverse aeration and unlimited fishing and netting of rough fish. Those strategies take time, and, in this situation, the small amount of rotenone used on the lakes is not enough to be of concern to citizens. The Minnesota Department of Health has also said the chemical has no long-term health risks.
Pesticides and other chemicals are not always the best way to eliminate unwanted species. But in certain situations, if used judiciously and under scrutiny, compounds such as rotenone can yield positive environmental benefits.
