Illinois ? A holding tank at a Caterpillar facility in a Chicago suburb broke Sunday, spilling about 65,000 gallons of oil sludge and contaminating a 3-mile section of the Des Plaines River, officials said.

The substance was reported to be hydraulic and cutting oil, said Maggie Carson, a spokeswoman for the Illinois Emergency Management Agency.

Most of the sludge spilled on land, but 6,000 gallons seeped into Des Plaines River water, U.S. Coast Guard Petty Officer William Mitchell said. He said the oil waste poses no risk to human health but could be dangerous to animals in the contaminated area.