Four ways in which water can be polluted are: chemical pollution, biological pollution, physical pollution, and sediment pollution. Chemical pollution occurs when harmful chemicals are released into water sources, such as pesticides, fertilizers, and industrial waste. Biological pollution occurs when harmful bacteria and viruses are introduced into water sources, such as from sewage and animal waste. Physical pollution occurs when physical objects, such as plastics and trash, are introduced into water sources. Sediment pollution occurs when soil and other materials are washed into water sources, which can harm aquatic life and affect water quality.