Introduction
A watershed is a surrounding land area that serves as drainage for a stream. It may cover a few acres of land surrounding a very small stream or includes large rivers. The quality of a stream depends on its watershed and human activities that occur there. The most common types of water pollution are bacteria, viruses, or protists, which are human pathogens, organic wastes, sediments, toxic chemicals such as pesticides, organic waste such as sewage and animal wastes, plant nutrients such as nitrates and phosphates, or heat, which causes thermal pollution.
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