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King County Water Quality Monitoring

The Water Resource Inventory Area (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 Griffin Creek along East Griffin Creek Road in the lower end of the Griffin Creek Valley. King County is not currently conducting benthic macroinvertebrate or stream sediment monitoring in the WRIA 7 Routine Streams Monitoring Program.


Griffin Creek is approximately 10,615 acres in size. It flows in a southwesterly direction from its headwaters to the Snoqualmie River floodplain and approximately three miles northwest to its confluence with the Snoqualmie River (Kaje, 2009).

Total land use in the Griffin Creek basin is mostly forest followed by scrub and wetlands. Other land use (barren land and grassland) and developed land account for less than 10% of land use. Nearly half of forestland is evergreen whiled development is mostly open space. Agriculture is not present in the basin. See Table 1 below for more details on land use.

Table 1. Total land use in the basin

Developed Forest Scrub Wetlands Other
Total 3% 63% 23% 6% 5%


Griffin Creek supports thriving steelhead and coho salmon populations, with both species ascending well into the headwaters. In addition, Chinook salmon utilize the lower reaches for spawning. Forested reaches are primarily composed of native riparian vegetation, which is important for providing shade for fish (King County, 2002).

Water Quality

Water quality samples are analyzed monthly for temperature, dissolved oxygen (DO), pH, conductivity, turbidity, total suspended solids, ortho-phosphorus, total phosphorus, ammonia, nitrate-nitrogen, total nitrogen, and fecal coliform (FC) 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. Griffin Creek is now categorized as “Core Summer Salmonid Habitat” for aquatic life use and “Primary Contact” for recreational use. As part of the updated water quality standards, portions of Griffin Creek have been assigned an additional “Supplemental Spawning and Incubation Protection” temperature criteria of 13 ºC to be applied from February 15th to June 15th. The Snoqualmie River is not listed on the Washington State Department of Ecology's (Ecology) 303(d) list for impaired streams. However, it does have EPA-approved Snoqualmie River Watershed Multiparameter and Temperature total maximum daily load (TMDL) plans in place and implemented to address fecal coliform (FC) bacteria and water temperature (Category 4a).

See Table 2 below for routine monitoring summary statistics of water quality data collected to date. If stormwater data is available for this site, it will be shown as Table 3. Historical data reviews can be found in the annual reports produced by METRO/King County DNRP.

To view charts of current water quality data, please visit the Data Download webpage.

Water Quality Index

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

Table 1. Routine monitoring summary statistics for this station from 2011 to 2022
ParameterNumber of SamplesMeanMinimumMaxmiumMedianStandard Deviation
Dissolved Oxygen (mg/L)13911.38.213.611.41.2
Temperature (°C)1399.32.417.49.24.0
Turbidity (NTU)1271.640.5614.201.271.45
Conductivity (mSIEMS/cm)13959.733.796.451.018.7
Total Suspended Solids (mg/L)1383.070.50120.001.7010.21
Ortho-Phosphorus (mg/L)1380.00770.00240.02960.00580.0047
Total Phosphorus (mg/L)1370.01800.00640.07300.01730.0085
Ammonia (mg/L)1380.00500.00210.01130.00470.0016
Nitrate (mg/L)1380.43590.14801.18000.32150.2561
Total Nitrogen (mg/L)1370.58730.25101.36000.48000.2634
Fecal Coliform(CFU/100ML)1222812601244


King County operates two stream gages on Griffin Creek: East Griffin Creek Road at the water quality monitoring site (22b) and approximately 700 feet upstream of the Fall City-Carnation Road Bridge (21a).

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 webpage.

While King County is not conducting benthic macroinvertebrate monitoring on Griffin Creek as part of the WRIA 7 Routine Streams Monitoring, both King County and Ecology collected benthic samples on Griffin Creek in 2012 and 2013. To see this data, please visit the Puget Sound Stream Benthos webpage.