The canal arose in the mid-19th century from local tidal wetlands and freshwater streams. By the end of the 19th century, heavy industrial use had caused large amounts of pollutants to drain into the Gowanus Canal. Various attempts to remove the pollution or dilute the canal's water have failed. Even though most industrial tenants stopped using the Gowanus Canal in the middle of the 20th century, the pollution was never remedied. By the 1990s, it was recognized as one of the most polluted bodies of water in the United States. Owing to pollution with high ratios of fecal coliforms, deadly proportions of pathogens, and a low concentration of oxygen, it is generally seen as incompatible with marine life. A variety of extremophiles have been observed in the Gowanus Canal as well.