The result can only be described as an ecological meltdown—particularly on Lake Michigan—previously unmatched in scope or speed. By 1962, biologists estimated the river herring accounted for 17 percent of the fish mass in Lake Michigan. Three years later that number was pegged at 90 percent. The exotic herring had similar success in Lakes Huron and Ontario, and took hold to a lesser degree in the colder and more sterile Lake Superior, and the warmer and more predator-filled Lake Erie.
