The city of Decatur says low water is what killed up to 10,000 Asian carp and other fish below the dam between Lake Decatur and the Sangamon River.
Keith Alexander is Decatur's water management director. He says the city lowered the water in part as a measure recommended by the Illinois Department of Natural Resources to help keep the carp out of the lake.
Alexander says high heat and the presence of so many fish in so little water is killing the invasive fish.
Alexander says 90% of the fish in the low-water area are carp. The city has never before noticed so many near the lake.
The fish have spread throughout the Mississippi, Illinois and Ohio river basins. They're heavy eaters that out-compete native fish for food.