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Surface Water Education
Stormwater Runoff
Stormwater runoff starts as rainwater that flows over the land into ponds, wetlands, streams, and eventually the Sammamish River and Lake Washington. Before the environment was disturbed by development, abundant trees and other vegetation helped to control this runoff.

The forests slowed down the rate that rain hit the ground, and unpaved land with plants and established root networks were able to absorb most of the runoff. This natural system prevented erosion and cleaned the rainwater through ground infiltration.

Runoff Today
Today, Mill Creek is quite different. When houses, streets, shopping centers, and businesses are built, natural soil and plants are replaced by hard or impervious surfaces, such as asphalt and pavement. When rain falls on these hard surfaces, it cannot soak into the ground, so it quickly becomes runoff.

The runoff ultimately drains into Mill Creek’s streams, increasing the water levels and washing debris, chemicals, and other kinds of pollutants into the area’s streams. Sediment from sources such as these can ruin spawning habitat for the fish that reproduce in our streams.

Water Quality
Water quality is also degraded by pesticides, fertilizers, cars that are dripping oil, residential car washing, pet waste, etc. Fish are harmed by the lack of shade over streams, which is needed to keep the water cool. The combination of sediment and other pollutants in stormwater runoff poses a real threat to Mill Creek’s streams and ponds.

Local Streams
In developed areas within Mill Creek, rain water runs into catch basins in the street and goes into our local streams.

Our major stream is called North Creek. We have four other streams, called tributary’s, in the city limits: Nickel Creek, Penny Creek, Mill Creek, and Sitka Creek. In older areas of the city, no water quality treatment is provided before the runoff enters the streams.

Sustainable Landscaping
Check out some sustainable landscape practices here