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King County Water Quality Monitoring

King County monitors the ecological health of the Sammamish River by collecting and analyzing surface water samples. Station 0486 is located at the Marymoor Park Bridge where Lake Sammamish drains into the Sammamish River. Sampling at this station began in 1971 and continues today. Station 0450 is located at the bridge on 68th Avenue Northeast in Kenmore where the river drains into Lake Washington. Sampling at this station began in 1971, but was discontinued in 2008 due to budget cuts. Station 0450CC, located where NE 145 crosses the Sammamish River, was added in 2009. The County also has stations along the major tributaries to the Sammamish River - Swamp Creek, North Creek, Bear Creek, and Little Bear Creek.

From time to time, additional studies have been conducted on the Sammamish River. Click here for information about Special Studies.


Water Shed Image

The Sammamish River basin drains a watershed composed of approximately 153,600 acres that includes 62,080 acres in the Lake Sammamish basin, 32,000 acres in the Bear Creek basin, and 42,880 acres that are the combined Little Bear, Swamp, and North Creek basins. The remaining 16,640 acres comprise the Sammamish River subbasin.

Historically, the Sammamish River was somewhat longer than it is today with abundant “swampy” areas that were filled with peat and diatomaceous earth. In 1891, the U.S. Army Corps of Engineers reported that the river was 17 miles long. The river corridor was heavily logged from the 1870s through the early 20th century. Throughout the 20th century, the river went through dramatic changes that reduced the complexity of the floodplain including the lowering of the Lake Washington, the channelization of the river, and the construction of drainage ditches in the river valley. The elevation of Lake Washington was lowered about 9 feet with the opening of the Chittenden Locks in 1916, and this elevation change drained much of the swampy Sammamish River corridor. Around the same time period, farmers in the Sammamish River Valley formed a drainage district that began to straighten the upper reach of the river dramatically. In 1962, The Corps of Engineers began to systematically dredge the river, primarily as a flood control project. Dredging the river deepened it 5 feet throughout most its length, which hardened the river’s banks, dramatically decreased its remaining connection with the floodplain, and cut off most of the smaller tributaries to the river. The Corps’ project also included the construction of a weir at the Lake Sammamish outlet. Overall, this project practically eliminated flooding in the Sammamish River Valley, and reduced the maximum flood elevations and seasonal water surface elevations in Lake Sammamish.

The Sammamish River is now about 13.5 miles long. The upper river corridor extends from the the Lake Sammamish weir in Marymoor Park to the City of Woodinville, Washington through a floodplain valley that is more than a mile wide in places. Land use in this upper reach includes open space and recreational areas at Marymoor Park, urban commercial and residential development in the City of Redmond, Washington the Willows Run Golf Course, the Sammamish Valley Agricultural Production District and urban development again in the City of Woodinville. The lower reach extends from Woodinville to the mouth of the riverat Lake Washington. This reach has a much narrower drainage area, which includes the downtown cores of Bothell and Kenmore but also some open space areas, including the Wayne and Inglemoor Country Club golf courses, Bothell parkland along the Sammamish River Trail, and King County-owned parcels at the mouth of Swamp Creek and the mouth of the river. A major King County sewer line runs underneath the Sammamish River Trail, which is adjacent to most of the river.

In total, just over half of the land use in the Sammamish River basin is forest and about a third is developed. Very little of the land is used for (pasture/hay) agriculture or consists of scrub and wetlands. Other land uses (barren land, grassland, and open water) makeup a relatively larger proportion of total land use in the basin. Forestland consists mostly of mixed forest while developed land is mostly low intensity and open space. 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 2% 31% 51% 2% 2% 12%


Chinook, coho, sockeye, kokanee, steelhead, and coastal cutthroat are known salmonid species that currently inhabit the Sammamish River system (Kerwin, 2002). The U.S. Fish and Wildlife Service has identified the river and its tributaries as potential foraging habitat for bull trout on the assumption that they are found in the watershed. Volunteers with the Salmon Watcher Program made observations at various locations within the Sammamish River basin from 1997 to 2015.

Two salmon-bearing tributary systems, Bear Creek and Little Bear Creek, are located in the upper reach. The lower reach includes two large salmon-bearing tributaries, Swamp Creek and North Creek (Kerwin, 2002).

Water Quality

Water quality samples are analyzed monthly for temperature, dissolved oxygen (DO), pH, conductivity, turbidity, total suspended solids, ortho-phosphate, 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. The Sammamish River 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 Sammamish River have been assigned an additional “Supplemental Spawning and Incubation Protection” temperature criteria of 16 °C. The river is on the Washington State Department of Ecology's (Ecology) 303(d) list for violation of water temperature, DO, FC bacteria, and pH standards (Category 5). DO levels decrease when the temperatures increase. In addition, high nutrient (phosphorus and nitrogen) concentrations can exacerbate low oxygen conditions by increasing vegetative growth. Decaying vegetation consumes oxygen in the water.

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 28-year (1979 – 2007) trend analysis was conducted with water quality data from both Sammamish River stations. Results indicated that water quality might have declined over this 28-year period with significant increases in water temperatures and conductivity, and decreasing DO concentrations. High conductivity can suggest the presence of unidentified dissolved charged substances in the water. Water at the mouth of the river is becoming less acidic as indicated by the significant increase in pH. (The pH remains within acceptable range relative to the state standards.) Decreased total suspended solids (TSS), turbidity, nutrients (ortho-phosphate and total phosphorus, ammonia and total nitrogen), and bacteria levels indicate some improvements in water quality in the same 28-year period.

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 2008
ParameterNumber of SamplesMeanMinimumMaxmiumMedianStandard Deviation
Dissolved Oxygen (mg/L)1839.25.813.38.81.7
Temperature (°C)32112.40.723.612.25.3
Turbidity (NTU)2783.150.3014.002.701.56
Conductivity (mSIEMS/cm)155147.2103.0204.0143.022.6
Total Suspended Solids (mg/L)2785.210.0044.904.303.99
Ortho-Phosphorus (mg/L)2780.02220.00440.06400.02020.0106
Total Phosphorus (mg/L)2780.04940.01500.15700.04830.0165
Ammonia (mg/L)2780.03740.01000.09690.03440.0186
Nitrate (mg/L)2770.46350.14001.11000.43600.1811
Total Nitrogen (mg/L)1960.77950.39401.60000.75150.2003
Fecal Coliform(CFU/100ML)277267127400150604

Table 2. Storm water monitoring summary statistics for this station from 1971 to 2008
ParameterNumber of SamplesMeanMinimumMaxmiumMedianStandard Deviation
Dissolved Oxygen (mg/L)158.87.611.08.31.1
Temperature (°C)1513.46.919.913.34.7
Turbidity (NTU)1539.122.28515.004.04131.71
Conductivity (mSIEMS/cm)15137.567.1178.0138.032.1
Total Suspended Solids (mg/L)1564.491.80850.004.40217.54
Ortho-Phosphorus (mg/L)150.02650.01420.04340.02840.0073
Total Phosphorus (mg/L)150.11170.04330.85000.06290.2045
Ammonia (mg/L)150.04860.02340.07640.05030.0166
Nitrate (mg/L)150.51210.21400.99100.39300.2425
Total Nitrogen (mg/L)150.94440.51502.43000.76900.5008
Fecal Coliform(CFU/100ML)159655464004901592


King County operates multiple stream and water temperature gages on the Sammamish River:

  • Streamflow: Sammamish River at Marymoor weir ( 51m), Sammamish River Transition Zone below weir ( Samm_TZ_1), Sammamish River Transition Zone mid ( Samm_TZ_2), Sammamish River above Bear Creek ( Samm_TZ_3), Sammamish River below Bear Creek ( Samm_TZ)_4), Sammamish River at 124th ( SAMM_124), Sammamish River bank repair NTU EA Primary 200 feet( SRBR_200), Sammamish River bank repair NTU EA Primary 200 feet 5' depth ( SRBR_200_...), Sammamish River bank repair NTU 5000 feet ( SRBR_5000), Sammamish River bank repair NTU compliance 3 mile ( SRBR_COMP), and Sammamish River bank repair NTU Contingency 4 mile ( SRBR_CONT)
  • Temperature: Sammamish River at West Park Entrance ( 51p) and Sammamish River south side in middle support of lower Woodinville RR bridge just above Little Bear Creek ( 51R)
The U.S. Geological Service also operates a stream gauge at NE 116th St ( 51T).

Stream Sediment

Benthic Invertebrates

Special Studies

Sammamish River Diel Dissolved Oxygen and pH Study

The study was designed to provide adequate spatial and temporal resolution of DO and pH along the river for use in modeling the Sammamish River. Stations at seven locations along the Sammamish River (including the upstream boundary) as well as one station on Big Bear Creek near the mouth were monitored.

Endocrine Disrupting Chemicals (EDCs) Survey

New information is emerging about the natural and synthetic chemicals people dispose of every day in their sinks and toilets. The purpose of this survey was to determine if EDCs would be found at detectable levels within the Elliott Bay/Central Puget Sound/Duwamish estuary and the lakes, major rivers, and some tributaries of the Green, Cedar, and Sammamish Rivers. Samples were collected at each location once per quarter in 2003; this method generated 4 samples per site collected throughout all seasons.

Sammamish River Sediment and Water Quality Assessment

The primary purpose of this assessment was to obtain baseline information and evaluate the concentration and distribution of potential contaminants of concern in Sammamish River surface water and sediment. Water sampling was conducted in early September 2001 and sediment sampling was conducted in early October 2001. Samples were analyzed for metals, organic compounds (including pesticides), and conventional parameters. In addition, water samples were analyzed for a number of parameters using U.S. Geological Survey's wastewater method that included analysis for chemicals classified as endocrine disrupters. Water quality monitoring was also conducted in the fall of 2002. Sediment chemistry and benthic community structure was conducted in 2003.

Sammamish River Corridor Action Plan

King County Department of Natural Resources and the U.S. Army Corps of Engineers were partners in the preparation of the Sammamish River Corridor Action Plan. The report was prepared in close coordination with local municipalities and stakeholders and provides guidance on restoration needs and projects for the Sammamish River Corridor. The plan focuses on the Sammamish River's role as a necessary migratory corridor for anadromous salmon in the Sammamish Watershed. The fundamental goal of the Plan is to make the Sammamish River Corridor a strong link, rather than a weak one, in this larger ecosystem.

Sammamish River Restoration at NE 124th

The goal of this project was to enhance riparian habitat by clearing invasive plant species and replacing them with natives. Contact Doug Chin for more information.

Water Resources Inventory Area (WRIA) 8

In WRIA 8, citizens, scientists, businesses, environmentalists and governments are cooperating on protection and restoration projects and have developed a science-based plan to conserve salmon today and for future generations.