The alewife is an anadromous species of eastern North America, a marine fish that uses freshwater streams for spawning. Alewives were first reported in Lake Ontario in the late 1800’s and in Lake Erie in the early 1930’s. By the early 1950’s populations had spread to all of the Great Lakes. Alewives inhabit the open lake waters during most of the year and move to shallow areas and ponds in the spring to spawn. Alewives often die in large numbers and dead and dying fish may drift in or be washed up on shore, littering beaches and harbors.

The alewife feeds primarily on zooplankton, reducing the available food for native fish species. Salmon, lake trout and other larger fishes prey upon alewives. Stocking of salmon species has helped to reduce alewife populations in the Great Lakes.