Storm sewer drainage and diesel fuel leaked into the Fox River in Elgin on Wednesday, according to local fire officials.
Authorities said Environmental Protection Agency personnel, as well as other federal and state officials, are on the scene while the response is underway.
Absorbent booms have been placed in the river to help absorb the fuel, with a hazardous materials company contacted to assist in containment efforts, officials said.
Although the source of the diesel fuel leak was unknown to authorities, cameras have been placed in the drains to help identify where the leak is coming from.
Officials did not have an estimate of how much fuel leaked into the river, adding that the leak is a “slow leak” and not a heavy flow.
According to the emergency services, the leak is “well contained” and there is no concern for the safety of nearby residents.
There was no further information available.