The U.S. Fish and Wildlife Service wants to find out how many sea lampreys are in the Detroit River.

A crew is expected to do an assessment from May 29th to June 7th that will help determine the need for measures to control the eel-like parasites.

They invaded the Great Lakes in the last century and decimated native fish until a poison was developed that brought them under control.

Sea lampreys attack fish such as trout, salmon and whitefish.