Colorado regulators say a damaged storage tank has dumped 7,500 gallons of crude oil into the Poudre River near Windsor.
Colorado Oil and Gas Conservation Commission spokesman Todd Hartman said Friday that oil has stained vegetation up to a quarter-mile away, but no drinking water intakes have been affected.
Officials say the bank where the storage tank sat on the river was undercut by floodwaters, causing it to drop and break a valve.
Noble Energy discovered the spill Friday and reported it to the oil and gas conservation commission.
Cleanup crews are trying to absorb the spilled oil, and a vacuum truck is removing oily water from a low-lying area near the tank.
Hartman says a second tank nearby appears to be unaffected.
Windsor is just southeast of Fort Collins.