As the runoff moves, it picks up and carries away natural and human-made pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters, and even underground sources of drinking water. Acid rain and changes to stream flow, such as dams and concrete channels, are also sources of nonpoint source pollution. Acid rain, much of which comes from cars and power plants, is rich in nitrogen, which can overstimulate the growth of aquatic weeds and algae. This in turn can deplete oxygen and kill aquatic life. Channelization reduces the ability of streams to assimilate or absorb waste and disturbs fish breeding areas.
Wetlands are areas of land that are wet at least part of the year.
Wetlands are populated by plants well adapted to grow in standing water or saturated soils. There are many different types of wetlands, including marshes, bogs, fends, swamps, prairie potholes, and bottomland hardwood forests. Wetlands may not always appear to be wet. Many dry out for extended periods of time. Others may appear dry on the surface but are saturated underneath.