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What is Stormwater?

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 such as to the Cowlitz or Coweeman rivers.

23rd Avenue - January 2009

Why is Stormwater a Problem in Washington?

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.

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. Urban development increases the amount of impervious surfaces such as pavement and rooftops. This increases water flow runoff and flooding frequency and intensity.  A typical city block generates 5 times more runoff than a woodland area of the same size.  Furthermore, because of the volume of runoff discharges, mass loads of pollutants in stormwater can be significant.

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.