History of Stream and River Monitoring Program

The King County Major Lake and Stream Monitoring Program is designed to protect the significant investment in water quality improvement and protection made by the people of King County. Sewage and wastewater used to be discharged directly into lakes Washington, Union, and Sammamish. Sewage and wastewater now enter secondary treatment facilities at West Point and Renton, from which clean, treated water is discharged into the well-mixed waters of Puget Sound. While the diversion of sewage resulted in dramatic improvements in lake water quality, monitoring water quality is still important.

With the removal of the majority of point sources of sewage effluent, non-point source pollution related to urbanization currently has the greatest impact on water quality. The long-term environmental impacts of non-point pollution on the quality of lakes and streams can only be evaluated by sampling at multiple sites throughout the watershed.

Streams and rivers in the King County service area are monitored as part of the routine monitoring program if sewer trunk lines cross them, or if they are considered a potential or significant source of pollutant loading to a major water body. (Information regarding the lake-monitoring program can be found at the King County Lakes web page.) Monthly baseflow samples have been collected at many of these sites since 1976. Parameters analyzed in the tributary samples include conventionals (flow, temperature, dissolved oxygen, pH, conductivity, turbidity, nutrients (phosphorus and nitrogen) and fecal coliform bacteria.

Beginning in 1987, storm samples were collected three to six times annually at the sites located at the mouth of streams. Wet weather sampling frequency was changed to quarterly at the mouth of the streams, and then it was eliminated in 2002. These storm/wet weather samples are analyzed for the same parameters as baseflow samples plus trace metals.

Sediment samples were collected annually at the same location as the storm/wet weather water sampling sites for analysis of trace metals. The stream sediment program was modified in 2004.

The most recent addition to the monitoring program is the collection of invertebrate benthos. Once each year these insects are collected from many of the stream monitoring sites.

The data from the stream monitoring program are analyzed with the following objectives:

• Characterize the general water quality condition of the stream
• Determine if applicable State and Federal water quality criteria are met
• Identify long-term water quality trends.