Water pollution is any contamination of water with chemicals or other foreign substances that are detrimental to human, plant, or animal health
According to the Environmental Protection Agency:
We all need clean water. People need it to grow crops and to operate factories, and for drinking and recreation. Fish and wildlife depend on it to survive.
There are different causes of water pollution. One major contributor is fertilizers containing nitrates and phosphates. In excess levels, these nutrients stimulate growth of algae and fungal plants. These algae blooms choke the life out of the water starving organims of oxygen and leading to dead zones where fish and sea life cannot survive.
Another major contributor is soil. While at first glance soil may not seem like a pollutant, it actually has some serious negative effects when washed into water bodies in large quantities. The excess soil in the water can block light so that plants die. It can clog the gilss of fish and soil can actually kill tiny animals and fish eggs.
There is also bacterial pollution that finds its way into our water sources. The bacterial pollution can come from sewage or food processing waste. According to the National Institute for Environmental Health Sciences - "Worldwide, nearly 2 billion people drink contaminated water that could be harmful to their health."