Water pollution occurs mostly when people overload the water environment with wastes. It's defined as contamination of streams, lakes, underground water, bays or oceans by substances harmful to living things. .
Water is necessary to life on earth. All organisms contain it, some drink it, some live in it. Plants and animals require water that is moderately pure, and they cannot survive if their water is loaded with toxic chemicals or harmful microorganisms. If severe, water pollution can kill large numbers of fish, birds, and other animals, in some cases killing all members of a species in an affected area. .
Pollution makes streams, lakes, and coastal waters unpleasant to look at, to smell, and to swim in. Fish and shellfish harvested from polluted waters may be unsafe to eat. People who ingest polluted water can become ill and if they"re exposed for a long time, may develop cancers, or have children with birth defects. .
There are two types of water pollution; point source and nonpoint source. Point sources of pollution occur when harmful substances are put directly into a body of water (such as an oil spill). A nonpoint source is when pollutants enter the water indirectly through environmental changes (like when fertilizer is carried into a stream by rain) .
The major water pollutants are chemical, biological, and physical materials that lessen the water quality. Pollutants can be separated into eight different classes: .
1. Petroleum Products - oil and chemicals from oil are used for fuel, lubrication, plastics manufacturing, and many other purposes. The petroleum products get into water by accidental spills from ships, tanker trucks, and leaky underground storage tanks. Many petroleum products are poisonous if ingested by animals and spilled oil damages the feathers of birds and the fur of animals, often causing death. .
2. Pesticides and Herbicides - chemicals used to kill unwanted animals and plants may be carried into streams by rainwater.
