Booms were being used in an effort to contain the spill near Milliken, The Denver Post reported. Anadarko Petroleum reported the spill Wednesday afternoon to the state Department of Natural Resources.
Inspectors were trying to determine the extent of oil spills into the river since the floods began last week, officials said. Dozens of oil and gas drilling and storage areas have been swamped or damaged, and empty oil drums were spotted earlier this week being carried downriver.
The South Platte, which drains much of the eastern slope of the Rockies in Colorado, joins the North Platte in western Nebraska. The river is a major source of water for domestic and agricultural use in Colorado.
Officials in Weld County in northeast Colorado said Saturday at least one pipeline was leaking into the South Platte and two others appeared to be at risk.
Gary Wockner of Clean Water Action said Colorado needs to rethink its approach to oil and gas drilling and fracking in floodplains in light of the floods.
"This state of Colorado and the U.S. Environmental Protection Agency must force Anadarko to clean it up -- no matter the cost -- and make reparations to the public, including paying fines and enforcing the Clean Water Act which may include civil and criminal penalties," Wockner said. "In addition, the state must initiate news rules for drilling and fracking near rivers, streams, and in floodplains that better protect the public and the environment."