Enforcement of these laws tends to be straight-forward because the source of pollution can be determined. A second major source of pollutants is nonpoint sources . Nonpoint sources are scattered over a large geographic area and come from a variety of places. These include sediments, animal wastes, pesticides and other materials carried by water from agriculture, municipal dumps and run-off. With nonpoint pollution, identifying a single responsible polluter is more difficult because it can come from a variety of sources.
Regulation is less effective and tends to rely on voluntary compliance.
In the past, the media have focused most closely on pollution from industrial wastes and their by-products. Extractive industries, like mining and forestry, produce acid mine drainage, brine and soil erosion. Although legislation has reduced the impact of these industries, by-products still pollute the water supply. Manufacturing industries often use toxic chemicals during production. Proper disposal of these chemicals can be very costly, and the temptation is great to dump them illegally.