'Large Fish Kill' At Oak Forest Lagoon: Park District

OAK FOREST, IL — A stench coming off of an Oak Forest lagoon, along with sightings of many dead fish over the weekend, has neighboring residents concerned.

The fish can be seen floating among algae in the water at Lagoon Park at Central Avenue and Leslie Lane. The lagoon is managed by the Oak Forest Park District, with oversight from an environmental company. A variety of fish live in the water, including bluegill, bass, carp and catfish. The pond has not been manually stocked in many years, said Oak Forest Park District Director of Parks & Recreation Kirstin Dahm.

Water samples were taken earlier this week, and park district officials consulted with both ILM Environments and the Illinois Department of Natural Resources in at attempt to pinpoint a cause for the casualties. Officials now believe the dead fish can be linked to a "dissolved oxygen event," they said Thursday in a release.

"Over the weekend, we experienced a large fish kill at the lagoon," park district officials said. "After lengthy discussions with ILM, the environmental company who oversees our algae treatments, and a biologist with the fisheries at the IDNR, we are suspecting there was a dissolved oxygen event at the lagoon which killed off many of the fish.

"... When the algae in the lagoon decomposes, bacteria consume oxygen to break it down which depletes oxygen levels in the water."

Changes in the oxygen level, officials said, could also be attributed to abrupt changes in water temperature.

"With recent rainfall and warmer weather, the lagoon may have warmed up; warm water holds less dissolved oxygen than cold water, therefore decreasing overall oxygen for aquatic life," the park district said. "Unfortunately, dissolved oxygen events usually kill off larger fish before the smaller fish, which explains why mainly large fish were found along the shores."

Maintenance crews are working to remove carcasses, officials said.

Water samples are being analyzed to ensure that there were no incidents with chemicals being added to the lagoon.

"It is stagnant gross water," one resident noted. "Notice the fountains weren't going and yes—looked really bad. Terrible. I'm sure it really smells bad for those neighbors."

Dahm said the fountains have not been used since 2016. The filters around the aerators would suck up the silt, causing the motor to burn out almost immediately.