Sludge is a 2005 documentary film by Appalshop filmmaker Robert Salyer chronicling the Martin County Sludge Spill that was an accident that occurred after midnight on October 11, 2000, when a coal sludge impoundment in Martin County, Kentucky, broke through an underground mine below, propelling 306 million gallons of sludge down two tributaries of the Tug Fork River. The movie documents the continuing story of the Martin County disaster, the resulting federal investigation, and the looming threat of coal sludge ponds throughout the coalfield region.