A fish kill discovered this week on the Little Vermilion River stretched from Mendota to seven miles downstream and was under investigation by the Illinois Department of Natural Resources and Illinois Environmental Protection Agency.
Low oxygen was detected in the river near Mendota and while this is likely the cause of the fish kill, the cause of the low oxygen was undetermined as of Wednesday, said Sgt. Phil Wire of the Illinois Conservation Police.
“It’s not known but a seven-mile stretch is not normal,” he said.
The EPA collected water samples Tuesday and Wednesday and will analyze them in a laboratory, which could shed more light on the source and cause, Wire said.
Dead fish were first reported to the DNR on Monday morning by a farmer and an initial assessment determined the kill stretched along seven miles of the small river.
On Tuesday, Wire and a fisheries biologist began counting and measuring dead fish. They finished this work Wednesday with the help of a second officer, Wire said.
Most of the dead fish were minnows, suckers, gizzard shad, sunfish and bass, he said.
In August 2014, a fish kill in Mendota Creek was attributed to a strong bloom of algae and low water, lowering the oxygen levels.
The Little Vermilion River watershed drains about 125 square miles of land, beginning north of Mendota, flowing south and emptying into the Illinois River at La Salle. From Mendota to La Salle, the river intersects with the Mendota, Vermilion and Tomahawk creeks. Mendota Creek is classified as impaired by the Illinois EPA, as is the Little Vermilion River at La Salle.