People began to notice the lack of large fish and the scars on others. Lampreys preyed on whitefish, lake trout and chub populations in lakes Superior and Michigan. The lamprey invasion made it hard on the people who fished the Great Lakes to make a living. One sea lamprey can upset an ecosystem and food chain by eating an estimated 40 pounds of fish or more in its lifetime. Because of lower large fish populations, small fish, like the alewife, were able to increase in numbers.
Alewives are also invader species which compete with native fish for food and habitat.
The chemical was not harmful to humans and didn't effect many plants, invertebrates, fish or waterfowl populations. The chemical worked, but it was costly and did kill some young fish. In 1958 biologists estimated that the Brule River in Wisconsin produced over 22,000 lampreys each year. The Great Lakes Fishery Commission said that this population made up 30-50 percent of all the lampreys captured on American tributaries. In 1986, DNR fish managers, technicians and engineers designed a new lamprey barrier which let fish migrate through to spawn, but captured the lamprey.