Contaminated water contains a chemical poison, a biological poison or an infectious agent. Physical pollution occurs as sand or soil turns the water cloudy or cyanobacteria bloom during summer and their remnants give the water a thick consistency similar to pea soup. Chemical pollution occurs when inorganic or organic waste enters the water. Biological pollution occurs when microorganisms from human waste, food processing and meat packing plants and medical facilities enter the water.
Microorganisms can alter the environment. As phosphate accumulates, the algae in the water will grow rapidly. The algal blooms supply nutrients to other microorganisms that use up the oxygen and multiply rapidly. Then the protozoa, small fish, crustaceans, and plants will die and land on the bottom of the ocean floor. The anaerobic bacteria like Desulfovibrio and Clostridium will thrive in the mud and produce such gases as hydrogen sulfide and carbon dioxide. The hydrogen sulfide gas gives the water the smell of rotten eggs. Algae produce the gas dimethyl sulfide, which is the strong smell all along the Sound in West Haven and New Haven.
Acid gases from the chimneys of factories and motor vehicles will mix with fog, rain and snow. This mix results in acid rain, which will damage forests and kill fish. Acid rain also contributes to the chemical weathering of rocks as described above and releases aluminum, which is washed into lakes, rivers, streams and oceans and causes fish to overproduce a sticky mucus. This sticky mucus will clog their gills, making it difficult for the fish to breathe. The polluted water will damage fish eggs and eventually all the fish will die off.
As it rains, animal wastes, paved surfaces, lawns and other areas that contain heavy metals, organic contamination and pesticides, release these pollutants which travel down the road and into the water. Thus, when it rains, this contaminated water becomes a part of the oceans, ponds and lakes and affect the plants, animals and fish, possibly killing some of them.