Water polluted with human and animal wastes can spread typhoid fever, cholera, dysentery, and other diseases. Most of the water in the U.S. is disinfected with chlorine to kill disease-causing germs. However, disinfecting does not remove harmful chemical compounds, such as polychlorinated biphenyls (PCB's) and chloroform, or harmful metals, such as arsenic, lead, and mercury. Sometimes, when chemicals seep into ground water, people who have PUMPS, pump up the water and then drink the water that is contaminated. The careless release of such toxic wastes, primarily into waste dumps, threatens ground water supplies. PCB's, chloroform, and pesticides have been found in some municipal drinking water. Scientists are concerned that drinking even small quantities of these substances over many years may have harmful effects. Pollution prevents people from enjoying some bodies of water for recreation. For example, odors and floating debris make boating and swimming unpleasant, and the risk of disease makes polluted water unsafe. Oil spilled from ships or offshore wells may float to shore. It can kill water birds, shellfish, and other wildlife. This creates a terrible problem, not only for animals but for people. Much of the worlds population lives near the sea, and commercial fishing is a very important industry for sea fairing people. When water becomes contaminated, it can kill entire populations of fish. Algae blooms can be triggered by the run off of certain phosphates that farmers use. These phosphates are rich in nutrients and can trigger blooms of algae. The algae then covers up the pond so that no light enters. The plants on the bottom die from lack of exposure to the sun. The algae also consume huge amounts of oxygen and just suck it right out of the water. This can kill the fish and other aquatic life in the pond, making the pond literally dead.
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