Toxic organic chemical, primary pesticide may be carry into the water in the surface runoff from agricultural areas. Perhaps the most dangerous type is the family of chemical called Chlorinated hydrocarbons. Common examples are known by there common chemical names as chlordane, Dieldrin, Heptachlor, and the famous DDT., which has been banned all over the world. They are very effective poison against insect that demand agriculture crops. Unfortunately, they can kill fish, birds, and animals, including humans. And they are not very biodegradable, taking more than 30 years in some cases to dissipate from the environment.