Causes of water pollution

 Pollution is also caused when silt and other suspended solids, such as soil, washoff plowed fields, construction and logging sites, urban areas, and eroded river banks when it rains.  Under natural conditions, lakes, rivers, and other water bodies undergo Eutrophication, an aging process that slowly fills in the water body with sediment and organic matter.  When these sediments enter various bodies of water, fish respirationbecomes impaired, plant productivity and water depth become reduced, and aquatic organisms and their environments become suffocated.  Pollution in the form of organic
material enters waterways in many different forms as sewage, as leaves and grass clippings, or as runoff from livestock feedlots and pastures.  When natural bacteria and protozoan in the water break down this organic material, they begin to use up the oxygen dissolved in the water.  Many types of fish and bottom-dwelling animals cannot survive when levels of dissolved oxygen drop below two to five parts per million.  When this occurs, it kills aquatic organisms in large numbers which leads to disruptions in the food chain.