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King County Water Quality Monitoring

King County monitors the ecological health of the Bear Creek basin in a variety of ways, including collecting and analyzing water, sediment, and benthic invertebrate samples. Routine collection of water quality samples began in 1971 and continues at station 0484 at the mouth of Bear Creek. Water samples were collected monthly from the two upstream sites, C484 and J484, from 1974 through 2008. Monthly water quality sampling resumed at station C484 in February 2013. Station 0484 is located approximately one mile upstream of the mouth of Bear Creek where it enters the Sammamish River (the first railroad bridge south of Redmond Fall City Road). Two upstream sites are located on the mainstem of Bear Creek. Station C484 is located at bridge number 119A on 95th Avenue (east of Avondale Rd). Station J484 is the furthest upstream site located at the bridge on 133rd (Seidel Rd), which is 100 yards east of Bear Creek Rd. Sediment samples have been collected annually at station 0484 since 1987. Benthic invertebrates have been sampled at various locations in the Bear Creek basin beginning in 1995.

From time to time, additional studies have been conducted on the Bear Creek basin. Click here for information about Special Studies.


Water Shed Image The Bear Creek basin is comprised of approximately 32,100 acres, which includes three sub-basins: Bear Creek (14,300 acres), Cottage Lake Creek (8,000 acres), and Evans Creek (9,800 acres). In total, there are over 100+ miles of streams including Bear Creek (approximately 12.4 miles), Cottage Lake Creek (approximately 6.7 miles), and Evans Creek (approximately 8.2 miles) (Metro, 1990; King County, 1989). There are nine lakes and over 2,000 acres of wetlands. Local jurisdictions within the basin include: unincorporated King County, unincorporated Snohomish County, City of Redmond, City of Sammamish , and the City of Woodinville, Washington.

The headwaters originate at elevations of 180 feet above sea level (Bear Creek) and 100 feet above sea level (Evans Creek). The confluence of the two creeks is at 50 feet above sea level. Bear Creek empties into the Sammamish River on the north side of State Route 520 in the City of Redmond. Widespread permeable gravel and sand fill the valleys of Evans and Bear creeks, allowing them to absorb water from local storm events and the inflowing tributaries (Metro, 1990; Kerwin, 2001).

Land use in the watershed has changed markedly in the past 150 years as development has increased. In 1985, the Bear-Evans basin consisted of 71% forest, 17% grass, 9% wetland, and 3% effective impervious surfaces (King County, 1989).

Currently, total land use is mostly developed and forest, with not much agriculture. Developed land is largely low intensity and open space; forestland is mostly evergreen and mixed; and agricultural land is used mostly for pasture/hay than cultivated crops. Wetlands makes up the third largest type of land use. Other types of land use (barren land, grassland, and open water) make up very little of the watershed. See Table 1 below for more details on land use.

Table 1. Total land use in the basin

Agriculture Developed Forest Scrub Wetlands Other
Total <1% 51% 40% 1% 5% >2%

A unique resource in the Bear Creek basin is the Cold Creek - Bassett Pond Natural Areas. A cold-water spring in this natural area, owned by King County, provides essential cool water to Cottage Lake Creek and the Bear Creek system during summer and early fall. Please visit the Cold Creek webpage to find out more about this natural area.


The Bear Creek Basin Plan, completed in 1990, designated Regionally Significant Resource Areas (RSRAs) along Bear Creek (King County, 1990). These areas exhibit high aquatic habitat and salmonid diversity and abundance and a demonstrated contribution to the regional fishery resource. Found in the basin are extensive freshwater mussel populations, freshwater sponges, river otters, crayfish, and a good representation of aquatic insects. Because of its diversity, the Bear Creek basin was distinguished as one of the top six natural resource basins in King County in the Waterways 2000 program. King County and the City of Redmond have facilitated construction of numerous stream restoration projects identified in the Bear Creek Restoration Plan.

The Bear Creek basin is known to have the following salmonids: Chinook, sockeye, coho, kokanee, coastal cutthroat, and steelhead (Kerwin, 2001). From 1996 to 2015, volunteers with the Salmon Watcher Program made observations at various locations in the watershed. In Bear Creek, volunteers consistently saw Chinook salmon, coho salmon, kokanee salmon, sockeye salmon and cutthroat trout.

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. Bear Creek and Evans Creek are now categorized as “Core Summer Salmonid Habitat” for aquatic life use and “Extraordinary Contact” for recreational use. As part of the updated water quality standards, portions of Bear Creek have been assigned an additional “Supplemental Spawning and Incubation Protection” temperature criteria of 13 ºC to be applied from September 15th to May 15th. Portions of Cottage Lake creek have been assigned an additional "Supplemental Spawning and Incubation Protection" temperature criteria of 16 ºC to be applied from September 15th to May 15th. Evans Creek and Bear Creek are on the Washington State Department of Ecology's (Ecology) 303(d) list for violations of bioassessment standards (Category 5). Both creeks also have two types of EPA-approved total maximum daily load (TMDL) plans in place and implemented: a Bear Evans Watershed Temperature and DO TMDL and Bear Evans Watershed Bacteria TMDL (Category 4a). Cottage Lake Creek has a Cottage Lake Total Phosphorus TMDL (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.

Long-term Trends

A trend analysis was conducted with water quality data collected from the creek. As with most streams in Water Resource Inventory Area (WRIA) 8, there has been a significant increase in water temperatures. Bear Creek’s water quality, while generally good, is challenged with high levels of FC bacteria, elevated water temperatures, and low DO levels.

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 these ratings compare with other stream sites, please visit the Water Quality Index webpage.

Table 1. Routine monitoring summary statistics for this station from 1971 to 2021
ParameterNumber of SamplesMeanMinimumMaxmiumMedianStandard Deviation
Dissolved Oxygen (mg/L)29010.56.514.110.61.2
Temperature (°C)43810.70.920.910.34.7
Turbidity (NTU)4054.580.40120.003.406.67
Conductivity (mSIEMS/cm)259128.772.7169.0129.021.5
Total Suspended Solids (mg/L)4408.410.60110.006.0010.18
Ortho-Phosphorus (mg/L)4400.02950.00360.72000.02370.0441
Total Phosphorus (mg/L)4400.06350.01601.15100.05110.0714
Ammonia (mg/L)4400.03710.00431.70000.01830.0975
Nitrate (mg/L)4400.58280.17801.50000.53000.2476
Total Nitrogen (mg/L)3410.89620.43001.92000.84100.2706
Fecal Coliform(CFU/100ML)4385872131001201389

Table 2. Storm water monitoring summary statistics for this station from 1971 to 2021
ParameterNumber of SamplesMeanMinimumMaxmiumMedianStandard Deviation
Dissolved Oxygen (mg/L)4510.38.213.710.01.3
Temperature (°C)619.91.817.410.03.6
Turbidity (NTU)5412.542.8655.409.9511.12
Conductivity (mSIEMS/cm)40113.355.0150.0115.521.2
Total Suspended Solids (mg/L)6231.243.60127.0023.5026.81
Ortho-Phosphorus (mg/L)620.03510.01200.11100.03050.0179
Total Phosphorus (mg/L)620.10740.03440.25100.08200.0567
Ammonia (mg/L)620.04860.00990.22000.03400.0452
Nitrate (mg/L)620.66080.26101.60000.59200.2332
Total Nitrogen (mg/L)601.21500.66102.00001.21000.3288
Fecal Coliform(CFU/100ML)6214153973006951586


King County operates several stream and water temperature gages on Bear Creek:

  • Streamflow: Bear Creek at Union Hill Road (02a), Bear Creek at 133rd Street NE near Redmond (02e), Bear Creek at Woodinville-Duvall Road (02f), Bear Creek at NE 162 (02f2), and Bear Creek at river mile 2.1 in Friendly Village Mobile Home Park (02R)
  • Temperature: Little Bear Creek located on north side of bridge off Maltby Road at river mile 5 (30E) and Bear Creek above Evans Confluence (BC0105A)

Stream Sediment

Sediment data were collected since 1987 from 0484 in Bear Creek as part of the Stream Monitoring Program. Data from 1987 through 2002 were analyzed, but no significant trends were identified for any of the parameters tested.

Sampling at the legacy site continued until 2010. A basin-wide sampling effort took place in 2006, including 12 collections along a 12 mile reach of Bear Creek. The nickel concentrations at sites 0484 and Q484 were above Sediment Cleanup Objectives (SCO). The concentration of pentachlorophenol (an organochlorine pesticide) found at site Q484 was also above the SCO. Effects associated with these chemicals are uncertain. Additional data were collected (AVS/SEM ratios) that suggest metals at site 0484 are bioavailable, but not at site Q484.

Station Q484 is located in a slow moving marshy wetland area of the creek. The sediments at this station are 22% fines, indicating that fine sediments as well as contaminants can accumulate in this area. It is not clear what sources could have contributed contaminants at this site as the upstream area is rural residential and mostly undeveloped.

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. To see the benthic macroinvertebrate data for Bear Creek, please visit the Puget Sound Benthos webpage.

Special Studies

Bear Creek Watershed Management Study

The Bear Creek Watershed Management Study report, formerly referred to as a Watershed-Scale Stormwater Plan, of the Bear Creek Basin in the Greater Lake Washington (WRIA 8) outlines recommendations to restore Bear Creek to existing and designated uses, so that it provides a healthy environment for the community and aquatic species.

Small Streams Toxicity/Pesticide Study

As part of King County's Small Streams Toxicity/Pesticide Study, pesticide concentrations and toxicity were measured in Bear Creek in 2001. The County collected samples for analysis of pesticides, other organics, metals, suspended solids, and toxicity (Ceriodaphnia dubia and Selenastrum capricornutum).

Investigation of Western Pearlshell Mussel (Margaritifera falcata) Mortality in Bear Creek, King County, Washington: A Disease Ecology Approach

King County conducted stream habitat assessments in 2001 in Bear Creek and Cottage Lake Creek to characterize the habitat quality, primarily for salmonids. During this habitat assessment, notations were made of freshwater mussel locations, numbers, size, and mussel-bed substrate. This report is intended as a preliminary reconnaissance of the mussel presence in the Bear Creek Basin. Additional surveys were completed in 2004.

Bear Creek Basin Planning

Numerous studies have been conducted in conjunction with basin planning and salmon conservation efforts. King County produced the Bear Creek Basin Current and Future Conditions Analysis Report in 1989 and the Bear Creek Basin Plan in July 1990. More recently King County, in partnership with Snohomish County, the City of Redmond, the City of Woodinville, and Washington State Department of Transportation, is working on the Bear Creek Watershed-Scale Stormwater Plan.