By The Associated Press

PORTAGE — About 200 fish that were found dead Sunday in a northwestern Indiana river likely died due to natural causes, state wildlife officials said.

The shad were found near a Portage, Indiana, marina along the East Branch of the Little Calumet River and all indications point to the fish dying from “a natural event,” said James Brindle, communications director for the Indiana Department of Natural Resources.

Shad appears to be the only fish species affected, and no other negative effects on wildlife — including birds eating the shad — have been observed, he said.

The DNR says that shad die-offs are common in Indiana winters, especially when the temperature suddenly drops from the 30s and 40s to well below freezing — as happened last week in northwest Indiana, The (Northwest Indiana) Times reported.

The Indiana Department of Environmental Management is expected to conclusively determine the cause of the fish kill in coming days.