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King County Water Quality Monitoring

The Watershed Resource Inventory Area 7 (WRIA 7) Routine Streams Monitoring Program was established during 2011 and consists of twelve sampling sites that are distributed throughout the Snoqualmie and Skykomish watersheds. Historically in King County, routine streams monitoring has been centered on WRIA 8 (Lake Washington/Cedar/Sammamish) and WRIA 9 (Green-Duwamish). However, in 2011, a Surface Water Management (SWM) fee increase allowed King County to expand its regular water quality monitoring efforts to include the King County portions of the WRIA 7 drainage. Objectives of this program are focused on quantifying long-term water quality trends to help inform the management of salmon recovery efforts, land use regulation, and to prepare for expected increases in climate variability.

King County collects monthly water quality samples on Harris Creek just downstream of the Route 203 bridge where Harris Creek enters the Snoqualmie Valley. King County is not currently conducting benthic macroinvertebrate or stream sediment monitoring in the WRIA 7 Routine Streams Monitoring Program.


Water Shed Image

The Harris Creek sampling site drains 5361 acres comprised primarily of a broad upland terrace that features extensive wetlands as well as several lakes and ponds. Most of the subbasin is dominated by forestry land use on both State-owned and private forest lands. Approximately 6% of the subbasin comprises rural residential land uses, with the remaining 18% in agriculture. The highest residential densities are associated with the shoreline development of Lake Joy and Lake Marcel. The entire subbasin is served by on-site septic systems (Kaje 2009).


The documented distributions of coho salmon and steelhead extend into the upper watershed where extensive wetlands and ponds likely provide excellent rearing habitat. Chinook salmon are presumed to utilize floodplain portions of the stream as juveniles, but spawning is not known to occur in Harris Creek. Coho salmon are also known to ascend Stillwater Creek as far as the Lake Marcel outlet.

Water Quality

Water quality samples are analyzed monthly for temperature, dissolved oxygen, pH, conductivity, turbidity, total suspended solids, ortho-phosphorus, total phosphorus, ammonia, nitrate-nitrogen, total nitrogen, and fecal coliform bacteria. Results are compared to state water quality standards. Water quality standards are designed to protect public health and aquatic life. Comparing monitoring results to water quality standards allows an understanding of how safe the creek is for recreational contact as well as for aquatic life. (See link at top of page to view current water data.)

State water quality standards were revised in 2003. Harris Creek is now categorized as “Core Summer Salmonid Habitat” for aquatic life use and “Primary Contact” for recreational use under the 2003 rules. A short reach of Harris Creek just upstream of Route 203 is listed on the 2012 Washington State Department of Ecology's (Ecology) 303(d) list as a "waters of concern" (Category 2) for fecal coliform bacteria, though no major violations of have been observed on the Tolt River.

Water Quality Index

A Water Quality Index (WQI) rating system was developed by the State Department of Ecology that evaluates several water quality parameters and gives a single rating of “high,” “moderate,” or “low” water quality concern. To see how Harris Creek ratings compare with other stream sites, visit the Water Quality Index page.

Table 1. Routine monitoring summary statistics for this station from 2011 to 2018
ParameterNumber of SamplesMeanMinimumMaxmiumMedianStandard Deviation
Dissolved Oxygen (mg/L)8711.29.113.311.21.1
Temperature (°C)879.42.614.79.73.3
Turbidity (NTU)762.790.5313.002.221.89
Conductivity (mSIEMS/cm)8769.038.9110.060.922.2
Total Suspended Solids (mg/L)877.010.8045.703.408.39
Ortho-Phosphorus (mg/L)860.00920.00320.02720.00710.0056
Total Phosphorus (mg/L)860.02350.00870.17600.02160.0183
Ammonia (mg/L)870.00580.00230.01610.00540.0026
Nitrate (mg/L)870.56120.28900.88800.54200.1476
Total Nitrogen (mg/L)860.75020.51001.12000.74100.1322
Fecal Coliform(CFU/100ML)873915501882


King County maintains one stream gage on Harris Creek (22a). The gage is located upstream of the water quality monitoring site, where NE 108th Street crosses Harris Creek.

Benthic Invertebrates

Benthic macroinvertebrates are small animals visible to the naked eye (macro) that lack a backbone (invertebrate) and live in or around the streambed (benthic). This group includes aquatic insects (such as mayflies and dragonflies), crustaceans, clams, snails, and worms. Benthic macroinvertebrates are of interest to scientists and water resource managers because they are an excellent indicator of the biological health of stream ecosystems and are a critical component of the food web in aquatic communities. Scientists quantify the composition and diversity of benthic macroinvertebrate populations in a stream to compare the biologic integrity of different streams. King County has utilized benthic macroinvertebrate sampling to assess biological health of numerous creeks across the county (see map).

For more information about benthic macroinvertebrates and King County’s Benthic Macroinvertebrate Program, please visit the King County Stream Bug Monitoring web page.

While King County is not conducting benthic macroinvertebrate monitoring on Harris Creek as part of the WRIA 7 Routine Streams Monitoring, King County (Roads) did collect benthic samples at two locations on Harris Creek in 2010. To see this data, please visit the Puget Sound Benthos webpage.