The state Department of Natural Resources says workers have nearly completed the cleanup of oil that polluted 10 to 15 miles of the North Raccoon River downstream from Jefferson.
The DNR says in a news release Friday that although the cleanup is nearly done, rain or snowmelt could cause small amounts of oil to seep into the river. Booms will be kept along the river to capture the oil.
DNR environmental specialist Alison Manz says a sheen remains in some areas along the shore.
The spill happened in mid-September, when the valve on a storage tank malfunctioned, releasing thick, black smelly used motor oil on to the ground.
The oil was held in a 20,000-gallon above-ground tank at Krieger's Greenhouse in Jefferson.