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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), and station J484 is the furthest upstream site located at the bridge on 133rd (Seidel Rd), 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 in the Bear Creek basin. Click here for information about Special Studies of Bear Creek.


Water Shed Image The Bear Creek basin is comprised of approximately 32,100 acres that includes three sub-basins: Bear Creek at 14,300 acres, Cottage Lake Creek at 8,000 acres, and Evans Creek at 9,800 acres. All together there are over 100+ miles of streams including Bear Creek at approximately 12.4 miles, Cottage Lake Creek at approximately 6.7 miles, and Evans Creek running approximately 8.2 miles (Metro 1990; King County 1989). There are nine lakes and over 2000 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.

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 much of the 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 in the area has increased. What was once primarily forest has become a mix of forest, grass, and impervious surfaces. In 1985 the Bear-Evans basin consisted of 71 percent forest, 17 percent grass, 9 percent wetland, and 3 percent effective impervious surfaces (King County 1989).

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 plan.aspx Cold Creek - Bassett Pond Natural Areas .

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). Since 1996 volunteers with the Salmon Watcher Program have been making observations at various locations in the watershed. In Bear Creek volunteers have consistently seen chinook salmon, coho salmon, kokanee salmon, sockeye salmon and cutthroat trout.

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. Bear Creek is 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 °C to be applied from September 15th to May 15th. Bear Creek, Cottage Lake Creek, and Evans Creek are all on the Washington Department of Ecology's (Ecology) 303(d) list, Category 4a, for having an approved TMDL plan for temperature, dissolved oxygen, and fecal coliform bacteria. See Table 1 for a summary statistics for the routine water quality data collected at this site. If stormwater samples have been collected at this site, they will be summarized in Table 2.

Long-term Trends

A 37-year (1971-2007) trend analysis was conducted with water quality data collected from all sites in the Bear Creek basin. As with most streams in WRIA 8, there has been a significant increase in water temperatures and an increase in conductivity at all Bear Creek stations over this time period. There were some improvements in water quality as evidenced by the decrease in total suspended solids (TSS), ortho-phosphorus concentrations, ammonia, and fecal coliform bacteria. To find out more information about the results of this long-term trend analysis for these sites, please view the summary table on the Water Quality Trends page.

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 view WQI scores for the Bear Creek stations visit the Water Quality Index page. You can also access site specific WQI reports from the Streams List or the Water Quality Index links on the left.

Table 1. Routine monitoring summary statistics for this station from 1971 to 2018
ParameterNumber of SamplesMeanMinimumMaxmiumMedianStandard Deviation
Dissolved Oxygen (mg/L)25710.56.514.110.51.2
Temperature (°C)40510.70.920.910.34.7
Turbidity (NTU)3734.660.40120.003.466.89
Conductivity (mSIEMS/cm)226127.976.0168.0128.520.9
Total Suspended Solids (mg/L)4088.700.60110.006.3010.43
Ortho-Phosphorus (mg/L)4080.03030.00360.72000.02420.0456
Total Phosphorus (mg/L)4080.06480.01601.15100.05210.0738
Ammonia (mg/L)4080.03930.00431.70000.02000.1015
Nitrate (mg/L)4080.59380.17801.50000.53250.2498
Total Nitrogen (mg/L)3090.91030.44301.92000.84400.2724
Fecal Coliform(CFU/100ML)4086222131001321433

Table 2. Storm water monitoring summary statistics for this station from 1971 to 2018
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 maintains four streamflow gauges in the Bear-Evans basin: Bear Creek at mouth (02a), Wetland Big Bear Creek #45 Outlet (02b), Bear Creek at 133rd ST NE, near Redmond (02e), Bear Creek at Woodinville-Duvall Rd (02f). King County also maintains one water temperature gauge: Bear Creek at Mouth (02j).

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 twelve collections along a twelve 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 a site Q484.

Station Q484 is located in a slow moving marshy wetland area of the creek. The sediments at this station are 22 percent fines, indicating that fine sediments as well as contaminants can accumulate in this area. It’s 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 web page. To see the benthic macroinvertebrate data for Bear Creek, please visit the Puget Sound Benthos webpage.

Special Studies

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). For more information, visit the pesticide study web site.

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. For more information about work in the Bear-Evans Creek Basin please visit the Sammamish Watershed page.

Freshwater Mussel Assessment of Bear and Cottage Lake Creeks in 2001.

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