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			What "Point" and "Nonpoint" Pollution Means Water pollution is classified by two general categories, called "point source" and "nonpoint source." As its name implies, point source pollution is discharged from a single point or pipe. Such pollution -- chemical and biological -- can be measured because the source is known and concentrated. State and federal water quality laws are designed to reduce point source pollution into waterways by requiring the businesses and government agencies that produce it to obtain permits, and by regulating the amount of contaminants discharged. Nonpoint pollution, or runoff, does not come from a fixed pipe or point. Rather it is the accumulation of soil, sand, sediments, chemicals, organic wastes and other pollutants on the land which are washed into streams, rivers, and lakes by rainfall and melting snow. Another form of nonpoint pollution cycles through the atmosphere. Toxic substances such as mercury, pesticides, sulfur dioxide, and a range of other air pollutants produced by cars, homes, businesses, power plants, and factories condense in precipitation into waterways. In most cases authorities seek to control nonpoint pollution through voluntary incentives, by writing ordinances that require natural buffer zones along shorelines, and by repairing eroding banks and road crossings. State and federal laws also contain provisions to prevent nonpoint pollution by conserving wetlands, which naturally absorb rain and purify runoff, and by prohibiting discharges of sediments and soil from construction sites. But the enforcement of these laws in Michigan is weak and inconsistent, and in many cases the fines are too low to be deterrents. (See the case study on pages 26, 27.) The federal Clean Air Act is intended to reduce the level of contaminants in the air, although progress is slowing as people drive more cars for longer distances, and Michigan and other Midwest states fight to prevent the U.S. Environmental Protection Agency from tightening standards. ~K.S.