Water polluted with human and animal wastes can spread typhoid fever, cholera, dysentery, and other diseases. The careless release of these toxic wastes, primarily in waste dumps, is seriously threatening ground water supplies. PCB’s chloroform and pesticides have been found in drinking water supplies in many countries. Pollution prevents people from using and enjoying water for recreation.

The oil can cause serious pollution and kill water birds, shellfish, and other wildlife. In addition, water pollution affects water-using activities and sports.

Water pollution also upsets various processes that occur naturally in water. These processes, which use the oxygen dissolved in water, help to make wastes harmless. Aerobic bacteria use oxygen in the water when breaking down organic wastes. This measurement is called the biochemical oxygen demand (BOD) of the water. Too many nutrients in water may lead to a process called eutrophication. Thermal pollution can also reduce the amount of oxygen that dissolves in water. Eutrophication, a process that affects lakes and other bodies of water, makes the quality of the affected water deteriorates until it becomes unfit for use by human beings. As we know, bodies of water support a natural cycle of life processes. The bacteria break down the body wastes of fish, releasing such nutrients as carbon dioxide, nitrates, and phosphates. Plant-like organisms called algae feed on these nutrients. Microscopic animals called Zooplanktons eat the algae, and fish eat the zooplankton. Fish obtain food and oxygen from the algae. People upset the balance when they pollute the water with excess nutrients. Thick layers of algae, called algae blooms, soon spread over the surface of the water. When the oxygen supply in the water becomes too small, fish and other water animals die. The dead fish and other wastes sink to the bottom of the water and form a layer of soft mud. As the mud becomes thicker, the lake gradually shrinks. The lake may turn into a swamp.