Several communities along the St. Clair rely on the river as their primary source of drinking water. About one-third to one-half of the residents of Michigan receive their water from the St. Clair/Detroit River waterway. Industries including petroleum refineries, chemical manufacturers, paper mills, salt producers, and electric power plants also need high-quality water for their operations. Since the late 20th century and passage of environmental laws to protect air and water quality, there have been occasional incidents when some of these industries have illegally contaminated river waters after discharging pollutants. Major clean-up activities were required.