Washington Waters > Stormwater

Learn about Stormwater

What is stormwater runoff?

Stormwater is rain and snow melt that runs off surfaces such as rooftops, paved streets, highways, and parking lots. As water runs off these surfaces, it can pick up pollution such as: oil, fertilizers, pesticides, soil, trash, and animal waste.

From here, the water might flow directly into a local stream, bay, or lake. Or, it may go into a storm drain and continue through storm pipes until it is released untreated into a local waterway.

In addition, the large impervious surfaces in urban areas increase the quantity of peak flows of runoff, which in turn cause hydrologic impacts such as scoured streambeds channels, instream sedimentation and loss of habitat. Because of the volume of runoff discharges, mass loads of pollutants in stormwater can be significant.

Human Health: In general, untreated stormwater is unsafe. It can contain toxic metals, organic compounds, bacteria, and viruses. Untreated stormwater is not safe for people to drink and is not recommended for swimming. Polluted stormwater can lead to beach closures for swimming and shellfish harvesting. It can also trigger toxic algal blooms.

Drinking Water: In some areas of Washington, notably Spokane County, and parts of Pierce and Clark counties, gravelly soils allow rapid infiltration of stormwater. Untreated stormwater discharging to the ground could contaminate aquifers that are used for drinking water.

Degraded Water Quality: Virtually all of our urban creeks, streams, and rivers are harmed by stormwater pollution. Stormwater is the leading contributor to water quality pollution of urban waterways in Washington.

Impaired Habitat: In Washington, urban stormwater harms and pollutes streams that provide habitat for fish and wildlife. Alterations to the watershed, such as building homes and other structures and clearing away trees and shrubs, are the leading causes for stormwater pollution.

Federal agencies identified habitat loss from stormwater runoff as one of the primary obstacles to salmon recovery.

How does stormwater pollute our streams?

Ever wondered where rain water or stormwater goes after it enters a storm drain? Find out where it goes by exploring this animated image. Have Fun!
(Courtesy of Chittenden County Vermont Regional Stormwater Education Program.)