Each time it rains, the potential for a pulse of polluted water to wash into local aquatic habitats is high. Pollutants such as pesticides, fertilizers, oil, animal feces, litter and even dirt can be picked up by rainwater and delivered to lakes, rivers and the ocean through storm drains and gutter systems. The effects of this contaminated water can impact multiple components of these ecosystems.

Habitat Degradation

Dirt is the number one cause of pollution in rivers and streams in the United States. When sediments from storm water settle to the bottom of a stream, river or lake, the quality of the habitat is severely impacted. The particles may cover spawning beds, block light from submerged aquatic vegetation or fill in pools used for fish habitat -- all of which can result in massive declines in fish populations. In addition, sediment deposits in waterways can reduce water depth, alter the flow of water, and carry in other toxic pollutants that can poison the habitat.

Altered Water Chemistry and Reduced Biodiversity

Pollutants such as sewage, fertilizers and agricultural runoff can increase the levels of nitrogen and phosphorus within aquatic habitats, upsetting their natural ecological balance. The consequences of increased nutrient loading are wide ranging. The algal blooms, depleted inorganic carbon, elevated pH and extremely low oxygen levels precipitated by these nutrients can result in reduced biodiversity within these habitats. The effects of nutrient loading, or eutrophication, threaten commercial and recreational fisheries worldwide.

Health Hazards

Polluted water can pose serious health risks, not only to the animals that inhabit the area, but also to the humans that rely on these resources for drinking water and recreational activities. When pesticides, solvents and used motor oil wash into aquatic environments, they can poison aquatic life. In some cases, chemicals may accumulate in aquatic species, causing adverse health effects in their predators or in humans that consume them. Furthermore, when bacteria and other pathogens are washed into recreational areas, beach closures may become necessary to prevent human health risks such as ear and eye discharges, skin rashes, and gastrointestinal problems.

Drinking Water Contamination

View of a dam

Storm water pollution of drinking water supplies is a common concern for water suppliers in urban areas. This is due to increased impervious surfaces, such as rooftops, roads and parking lots, that collect pollutants and quickly transmit them to receiving waters after a storm. These pollutants reduce the water quality in aquatic systems that provide drinking water and can be linked to illnesses in exposed populations. Nineteen percent of the population of the United States is dependent on public drinking water supplies that have reported health violations.