Development and urbanization can lead to increased stormwater runoff and pollutants because of impervious surfaces (rooftops, driveways, streets and parking lots) which prevent rainwater from soaking into the ground and allow stormwater to pick up chemicals, dirt, and other pollutants and wash them into storm sewers.

Stormwater runoff from construction activities can have a significant impact on water quality as well. As stormwater flows over a construction site, it picks up pollutants like sediment, debris, and chemicals.

Activities at industrial facilities, such as material handling and storage, are often exposed to precipitation and stormwater. Rain and snow falling on these materials pick up pollutants and transport them to nearby storm sewer systems.

A decline in population of aquatic plants and animals can also be caused by improper stormwater and watershed protection. Sediment clouds the water, destroys aquatic habitat, and increases water treatment costs. Lawn fertilizers can cause algal blooms, bacteria and other disease-causing organisms can wash into water bodies and create health hazards, and hazardous chemicals such as oil, household pesticides, auto fluids, and paint solvents can poison aquatic life.

Improper stormwater and watershed protection can also lead to a loss of recreation and increased costs for treatment, maintenance, and regulatory compliance.

A common misconception is that stormwater runoff from streets and parking lots goes to a wastewater treatment plant. In fact, stormwater usually receives no treatment and if it flows through a storm sewer it's headed straight into the rivers and streams we use for boating, swimming and drinking water.