King County logo

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 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.


Griffen Creek (10615 acres) is a predominantly forested subasin that generally flows in a southwesterly direction from its headwaters until it reaches the Snoqualmie River floodplain where it trends to the northwest for approximately three miles to its confluence with the Snoqualmie River (Kaje 2009). Like many other tributaries in the watershed, the lowest reaches of Griffen Creek are within the agriculture production district (APD) which includes portions of the Snoqualmie’s 100-year floodplain. The watershed also contains a rural residential land use designation, and King County’s Griffen Creek Natural Area.


Griffen Creek supports thriving steelhead and coho salmon populations, with both species ascending well into the headwaters. In additions, Chinook salmon utilize the lower reaches for spawning. In the forested reaches, riparian vegetation is primarily composed of native species (King County, 2002).

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. Griffin Creek is now categorized as “Core Summer Salmonid Habitat” for aquatic life use and “Primary Contact” for recreational use under the 2003 rules. As part of the updated water quality standards, the creek has been assigned an additional “Supplemental Spawning and Incubation Protection” temperature criteria of 13 ºC to be applied from February 15th through June 15th. A short reach of Griffin Creek between the Route 203 bridge and its confluence with the Snoqualmie River is listed on the 2012 Washington State Department of Ecology's (Ecology) 303(d) list for violations of fecal coliform bacteria standards (Category 4a).

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 Griffin 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)8811.28.213.611.11.3
Temperature (°C)889.32.416.29.63.8
Turbidity (NTU)771.540.624.451.290.73
Conductivity (mSIEMS/cm)8859.435.896.451.218.2
Total Suspended Solids (mg/L)882.350.509.271.801.59
Ortho-Phosphorus (mg/L)880.00770.00260.02720.00580.0047
Total Phosphorus (mg/L)870.01680.00770.03550.01580.0062
Ammonia (mg/L)880.00490.00210.01010.00460.0016
Nitrate (mg/L)880.45590.15601.18000.33200.2568
Total Nitrogen (mg/L)870.61040.29801.36000.51800.2616
Fecal Coliform(CFU/100ML)882912601345


King County operates two stream gages on Griffin Creek. Gage 22b is located at the water quality monitoring site on East Griffin Creek road while 21a is located downstream, approximately 700 feet upstream of the Fall City - Carnation Road Bridge.

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 Griffin Creek as part of the WRIA 7 Routine Streams Monitoring, both King County and the Washington State Department of Ecology collected benthic samples on Griffin Creek in 2012 and 2013. To see this data, please visit the Puget Sound Benthos webpage.