Contamination of fresh- or saltwater with materials that are toxic, noxious, or otherwise harmful to fish and other animals and to humans, including thermal pollution. Disposal of untreated chemical and municipal wastes in streams and rivers has been illegal since the early 1900s; in 1973 the EPA prohibited dumping of all types of wastes into the ocean. Unintentional pollution results from runoff containing toxic insecticidal residues. Oil spills at sea are a continual problem and probably will remain so.See waste treatment; Environmental Protection Agency; Environmental Chemistry.