Dead catfish wash up on shore at Lake Mendota after a multitude of circumstances resulted in a fish kill. (Reporter photo)

MENDOTA – A drop in the oxygen level due to a number of circumstances resulted in numerous fish dying at Lake Mendota. The dead fish were first discovered on Sept. 28.

David Wyffels, Illinois Department of Natural Resources fisheries biologist, said the recent hot weather and several other bad things all came together to result in the fish kill.

He cited algae bloom as the main culprit. Algae bloom is a microscopic organism in the water that produces oxygen during the day through photosynthesis, but also uses oxygen at night when there is no photosynthesis occurring. The use of the oxygen by the algae bloom at night is depleting the amount of oxygen available in the lake water, thus suffocating the fish.

He added that there has not been any fresh water coming into the lake because of a lack of rainfall, so that combined with the extremely hot weather caused the growth of algae bloom.

“In a typical year you have fresh water coming through, so with the lack of rain and the hot temperatures, algae bloom can develop,” said Wyffels.

Carl Ambler, Streets and Parks Superintendent for the city of Mendota, set up a pumping system in which water was sucked from the lake into a pump and then directed back into the lake to resupply it with fresh water.

Wyffels said there have been other bodies of water in the state that have been experiencing the same issues, and that it’s really up to Mother Nature.

“It’s going to get better,” Wyffels said. “These things go on for several days and then balance themselves out.”