Water pollution occurs when pollutants are directly or indirectly discharged into bodies of water like lakes and rivers. It affects plants and organisms living in these waters and damages biological communities. Water pollution has many causes including chemicals released from smokestacks that fall into water sources as rain. It endangers human health by contaminating drinking water with pathogens from human and animal waste that can cause illnesses like typhoid, cholera, dysentery, polio and hepatitis. Around half of ocean pollution is sewage and other industrial waste, much of which is improperly disposed of in waterways.