Assessing the Environmental Health of Streams in Washington

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The burgeoning population and development of Washington’s Snohomish County makes it one of the fastest growing counties in the nation. The resulting changes to land use may cause health degradation to bodies of water across the county.


The State of Our Waters program is an integrated monitoring program that characterizes and tracks changes to stream health. To determine a stream’s health, biological, chemical, and physical data are collected at up to 40 randomly selected locations each year, using a stratified random sampling approach. Potential sites are stratified according to land use, such as noncommercial and commercial agricultural, forested, rural, and urban.

The 2015 high-resolution (1-meter) NOAA C-CAP land cover data have been highly valuable for determining the types of land cover along the stream buffers and in the selected subbasins that drain to streams. Differences in land cover characteristics are used to evaluate the influence of the county’s population growth and development changes on observed stream health conditions and variability.


Snohomish County is continuing to develop stream health reports, which began in 2018. The reports have helped the county focus resources to protect healthy waters and improve impaired ones. (2020)

Land cover classifications for the French Basin
Land cover classifications for the French Basin
An example of a State of our Waters Health Report from the French Creek
An example of a State of Our Waters health report from the French Creek

Contributing Partners