Background
 

Pollutants enter the watershed either directly from a traceable source (point source pollution) or through channels that prevent the source from being identified (non-source point pollution). Regardless of the manner in which they enter the water, pollutants can be classified into four types: toxic, sediment, nutrient, and bacterial.

Toxic pollution includes chemicals that poison and kill organisms in and near streams, rivers, lakes, and the Bay. When a body of water has a high level of toxic pollution, fishing for the purpose of human consumption is banned. Even low levels of toxicity can be lethal when chemicals accumulate in predators that consume large amounts of slightly poisoned organisms. Examples of toxic pollution include pesticides and herbicides; gasoline, oil, and other automotive products; household cleaning products; paints and solvents; battery acid; industrial waste chemicals; and toxic substances in car exhaust and solid waste incinerator smoke.

Sediment pollution is dirt, minerals, sand, and silt eroded from the land and washed into the water. It comes from areas where there is inadequate vegetation to slow runoff. Sediment causes several problems for aquatic organisms. First, particles of sediment are suspended in the water. The resulting cloudiness decreases the amount of sunlight that can reach underwater plants that provide food and oxygen for underwater animals. Second, as sediment particles settle, they fill spaces between rocks, destroying the habitat needed by manyunderwater insects and other macroinvertebrates. Sediment also clogs the gills of fish, crabs, and other underwater organisms. Sediment can bury fish and insect eggs, preventing them from hatching, and when it covers an oyster bed, it smothers the oysters.

Nutrient pollution results from an overabundance of nutrients such as nitrogen and phosphorus. Living things cannot survive without nutrients, but too much can be detrimental to watershed organisms. An overabundance of nutrients leads to escalation in plant growth, particularly of algae and vascular plants. This causes two problems. First, water clouded with too much alga growth does not allow enough sunlight to reach the plants below. Second, when those plants die, the bacteria that decompose them use inordinate amounts of dissolved oxygen. This deprives underwater animals of the oxygen they need to survive. Sources of nutrient pollution include overflow from sewage treatment plants, leakage from improperly maintained septic systems, discharge from factories, and automobile exhaust. Examples of nutrient pollutants include fertilizers, animal manure, discharge from boat toilets, and household detergents.

Bacterial pollution occurs when there is an excess of harmful bacteria. There are many beneficial bacteria in the water. Even harmful bacteria in small amounts are safe. In larger concentrations, however, certain types of bacteria can be deadly to fish and animals (including humans) that drink or accidentally ingest the water. Certain bacteria can cause illness if they come in contact with an open wound. Interestingly, most of these harmful bacteria do not affect aquatic insects. Some sources of bacterial pollution include overflow from sewage treatment plants, leakage from improperly maintained septic systems, animal manure, and discharge from boat toilets.

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