DETROIT, Jan. 29 (UPI) -- Researchers say gizzard shad dying in waterways around Detroit show signs of viral hemorrhagic septicemia, a disease that caused a major die-off four years ago.

Thousands of dead shad have been found in the St. Clair and Detroit rivers, Lake St. Clair, connected by the two rivers to Lake Erie and Lake Huron, and Lake Erie itself, the Detroit Free Press reports.


Michael Thomas, a biologist with the Michigan Department of Natural Resources, said low temperatures are also responsible for the deaths. He said either the virus makes the fish more vulnerable to the cold or vice versa.

Thomas said the size of this die-off has not been measured, although many fish carcasses can be seen under the ice. Most of the victims appear to be juveniles measuring 4 to 7 inches.

The virus was first detected in Lake St. Clair in 2003. The 2006 die off killed thousands of fish.