Introduction of chemical contaminants into a water body. Water pollution occurs when undesirable foreign substances are introduced into natural water.These foreign substances can consist of animal or human waste, toxic materials, bacteria, chemicals, acid rain, high temperature water from power and energy plants. Contaminants in water present great danger to humans, animals, and the crops that are exposed to them. Unwanted occurrences such as the growth of algae due to high temperatures can render the water to be unfit for consumption. Common sources of pollution include chemical wastes from factories, or oil leaks from pipelines, all of which can be controlled. Other sources that are less likely capable of being controlled are water sources that contain elevated levels of nitrates and runoff sediments, which each characterize as high degrees of pollution. These pollutants are difficult to identify and treat with a good chance of passing into aquifers or streams, covering a wide range.