Moreover, the DNR will not rehabilitate lakes where the rotenone treatment might affect an endangered species. Health concerns have also prompted some public criticism of rotenone applications. DNR biologists conduct careful environmental analysis before a treatment is planned. They monitor lake water temperature and chemistry, review records for rare or endangered species, and determine the prevalence of nontarget wildlife species. The timing of the chemical application, which is carried out by trained professionals, is done to reduce harm to any animals other than the targeted rough fish.
Rotenone kills by preventing gill-breathing fish, amphibians, and invertebrates from using oxygen.
A naturally occurring substance, rotenone has been used for centuries by native South American Indians to kill fish for food. Although toxic to fish living in the treated lake, rotenone breaks down to carbon dioxide and water within a few weeks, rendering it harmless. In the concentrations the DNR uses to treat lakes, rote-none is not toxic to humans or any wildlife that eats fish killed by the substance. In recommended doses, aspirin is a safe medicine, just as rotenone is safe in the levels we apply. But if you swallow an entire bottle of aspirin, you'll get sick or die.