State of Our Waters - Streams

Snohomish County is home to over 5,700 miles of rivers and streams flowing down from the Cascade mountains and into Puget Sound. The State of Our Waters program helps us understand the health of this vast network of streams that provide both natural beauty and important functions including:  

  • Recreation 
  • Fish and wildlife habitat 
  • Flood prevention 
  • Groundwater recharge for drinking water 
  • Pollution prevention

award image  Stream Health Report Cards


Find your stream health report by selecting a location on the interactive map below. Don't see your stream? Check back next year as new sites will be added each year. You can also visit our online database to view and download new and historic data which includes more stream locations. 

Monitoring Stream Health

Snohomish County looks at five key indicators to understand stream health. Three of the indicators, water quality, aquatic life, and habitat are summarized in the stream health report cards. The other two indicators, land cover and hydrology provide context to understand changes in health over time.

  1. Water Quality
  2. Aquatic Life
  3. Habitat
  4. Land Cover
  5. Hydrology
Water quality   

Water Quality

Water quality is a measure of the chemical and physical characteristics of the water that affect the streams health. Water quality includes measuring the chemical and physical characteristics of the water including the following eight parameters: 

 Temperature  pH Nitrogen  Turbidity
Dissolved oxygen Fecal coliform/E.coli Phosphorus Suspended sediment

The results are combined to calculate the streams Water Quality Index (WQI). The annual index score is an average of the three lowest scoring months. The score can range from 0-100 with higher numbers indicating better water quality. The WQI was developed by the WA State Department of Ecology and is used throughout the state to summarize water quality data in an easy-to-understand format. 

Which streams do we monitor?

Each year we randomly select 30-50 sites to sample. The sites are selected to represent the four major land use types in the area: urban, rural, forested, and agricultural areas. There are two types of sites:

  • Trend sites - used to track changes over time and help to us understand if changes are due to large-scale natural causes, like drought or local, watershed-level changes. To do this, the same 20 or so sites are sampled every year. 
  • Status sites - used to understand the conditions of specific streams. Each year approximately 15 status sites are sampled and over time collectively help to understand the larger stream system.

Photo of stream

Do you live near a stream? - we are here to help

As a streamside landowner you have a unique opportunity to help keep water clean, benefit wildlife habitat and improve flood and erosion control. Snohomish County has resources to help you protect your property and improve the health of our local waterways. For more information or to talk to our watershed steward visit our streamside living page.