WATER POLLUTION

There are many specific causes of water pollution, but before we list the toppers, it's important to understand two broad categories of water pollution:
“Point source” — occurs when harmful substances are emitted directly into a body of water.
“Nonpoint source” — delivers pollutants indirectly through transport or environmental change. An example of a point source of water pollution is a pipe from an industrial facility discharging effluent directly into a river. An example of a nonpoint-source of water pollution is when fertilizer from a farm field is carried into a stream by rain (i.e. run-off).
Point-source pollution is usually monitored and regulated, though political factors may complicate how successful efforts are at true pollution control. Nonpoint sources aremuch more difficult to monitor and control, and today they account for the majority of contaminants in streams and lakes.
Many causes of pollution, including sewage, manure, and chemical fertilizers, contain "nutrients" such as nitrates and phosphates. Deposition of atmospheric nitrogen (from nitrogen oxides) also causes nutrient-type water pollution.