Environmental contaminants staff from the East Lansing Field Office investigated a fish kill that apparently began sometime on Nov. 21, 2005, in the North Branch of the Ecorse River in Wayne County, Mich.  More than 40,000 dead fish were observed in the river downstream of where a covered drain enters it.  The U.S. EPA asked the Service and the state for assistance, and we determined that the dead fish were all gizzard shad between 12 and 15 cm in length.  We observed live fish of other species and mallards behaving normally in the immediate vicinity of the spill.  The dead fish appeared otherwise normal. 

Gizzard shad are known to be sensitive to sudden changes in water temperature.  The spatial distribution of fish suggests that gizzard shad may have been present in the drain when a sudden change of water temperature occurred.  The flow pattern of the drain suggests that it receives discrete flow discharges.  The most likely explanation of this sudden, localized fish kill is that the drain received a discharge flow at significantly different temperature (greater than +/- 10 degrees?) than the ambient water. 

The Michigan Department of Environmental Quality will look into known dischargers to the drain and determine if their discharge permits include temperature requirements and if any unusual discharges were made during the time period in question.