Sea lampreys in the Detroit River
In this photo taken July 16, 2010, a scientist with the Hammond Bay Biological Station near Huron Beach, Mich., holds a female sea lamprey.
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.