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King County Water Quality Monitoring

King County monitors the ecological health of Swamp Creek in a variety of ways, including collecting and analyzing water, sediment, and benthic invertebrate samples. Station 0470 is located at the U.S. Geological Survey gaging station near Bothell Way and 80th Ave North. Water quality samples have been collected monthly at this station since 1972. In 1999, the County began monitoring another site on Swamp Creek (BB470) located at Carter Road. Sampling at this site was discontinued in 2008 due to budget cutbacks, but resumed in 2014. Beginning in 1987, sediment quality samples have been collected from Swamp Creek. King County began collecting benthic macroinvertebrate samples in Swamp Creek in 2002.

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


Water Shed Image Swamp Creek originates in the Paine Field and West Casino Road area of South Everett, Washington. Extensive wetlands once dominated the headwaters of Swamp Creek. The upper reaches still have some large good-quality wetlands and high-quality salmonid spawning and rearing habitat, as well as one of the largest populations of freshwater mussels found in the Puget Sound Lowlands (King County WLRD, May 2001). The creek flows roughly 10.9 miles southward into King County, where it empties into the Sammamish River just upstream of its outlet into Lake Washington.

The Swamp Creek basin is approximately 15,000 acres, and roughly 52% of the drainage is impervious and 19% forested cover. The drainage basin includes Scriber Lake, Martha Lake, and Lake Stickney and drains portions of the Cities of Lynnwood, Everett, Brier, Bothell, Mountlake Terrace, Kenmore, and unincorporated Snohomish County.

Streambank stability was found to be generally poor throughout Swamp Creek during a habitat survey in 2001 (King County WLRD, May 2001a). Streambank stability ratings in many segments were related to the riparian corridor condition. Segments in the upper reaches of the watershed tended to have more stable streambanks than the middle and lower reaches.

Total land use in the Swamp Creek basin is predominantly developed followed by forest. Land is not used for agriculture. Scrub, wetlands, and other land uses (grassland and open water) amount to less than 4% of total land use. See Table 1 below for more details on land use.

Table 1. Total land use in the basin

Developed Forest Scrub Wetlands Other
Total 88% 8% <1% 3% <1%

The increased urbanization has resulted in peak flows of greater intensity and duration, lower summer flows, increased flashiness, over-widening of the stream channel, bank erosion, and scour of the streambed (Kerwin, 2002). Increased frequency of flood flows from 1964 - 1990 were found to coincide with urbanization over the same period.


From 1997 to 2015, volunteers with the Salmon Watcher Program recorded salmon observations at various locations in Swamp Creek. Volunteers consistently saw coho in the creek. Less commonly spotted were kokanee and sockeye salmon. Chinook salmon were not seen.

The salmonid habitat quality of Swamp Creek was evaluated by King County from August to November 1999 (see Special Studies section below). The middle stream reaches tended to be higher quality than the upper and lower segments. Most segments fell primarily in the low and medium-low habitat quality categories, although three segments were rated medium-high. Chinook redds were not found in Swamp Creek during the 1999 King County assessment (King County WLRD, 2000a); however, juvenile salmonids, including coho and cutthroat, were observed in many segments during the 1999 habitat surveys (King County WLRD, 2001a).

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. Swamp 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, the creek has been assigned an additional “Supplemental Spawning and Incubation Protection” temperature criteria of 13 ºC to be applied from September 15th to May 15th. Swamp Creek is on the Washington State Department of Ecology’s (Ecology) 303(d) list for violation of water temperature, DO, and bioassessment standards (Category 5). The creek has an EPA-approved Swamp Creek Bacteria total maximum daily load (TMDL) plan in place and implemented for FC bacteria (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 28-year (1979 – 2007) trend analysis was conducted with water quality data from station 0470 in Swamp Creek. Results indicated that water quality might have declined over this 28-year period with significant increases in water temperatures, total phosphorus, and conductivity. High conductivity can suggest the presence of unidentified dissolved charged substances in the water. DO concentrations have also decreased significantly. Water at the mouth of Swamp Creek is becoming more acidic as indicated by the significant decrease in pH (the pH remains within acceptable range relative to the state standards). Decreased total suspended solids (TSS), nutrients (ortho-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 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 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 2024
ParameterNumber of SamplesMeanMinimumMaxmiumMedianStandard Deviation
Dissolved Oxygen (mg/L)3349.86.713.99.91.6
Temperature (°C)46010.30.119.710.24.3
Turbidity (NTU)4293.230.2022.002.602.29
Conductivity (mSIEMS/cm)305185.199.1250.1186.932.0
Total Suspended Solids (mg/L)4645.110.5052.003.505.93
Ortho-Phosphorus (mg/L)4640.02660.00730.07900.02590.0104
Total Phosphorus (mg/L)4640.05570.00670.19700.05300.0207
Ammonia (mg/L)4640.02300.00560.12000.02030.0132
Nitrate (mg/L)4640.72740.16302.32000.67400.3491
Total Nitrogen (mg/L)3870.99880.38902.90000.95200.3389
Fecal Coliform(CFU/100ML)42927765600140563

Table 2. Storm water monitoring summary statistics for this station from 1971 to 2024
ParameterNumber of SamplesMeanMinimumMaxmiumMedianStandard Deviation
Dissolved Oxygen (mg/L)479.
Temperature (°C)629.
Turbidity (NTU)5610.891.60132.007.4717.43
Conductivity (mSIEMS/cm)32160.071.9217.0161.541.7
Total Suspended Solids (mg/L)6424.244.00155.0016.1024.00
Ortho-Phosphorus (mg/L)640.03140.00900.14100.02700.0188
Total Phosphorus (mg/L)640.09600.03530.29400.08260.0490
Ammonia (mg/L)640.03430.01010.20000.02590.0356
Nitrate (mg/L)640.70580.23602.00000.63300.3309
Total Nitrogen (mg/L)621.22210.62302.30001.19500.3196
Fecal Coliform(CFU/100ML)64187155240009003228


King County maintains two water temperature gages and on stream gage on Swamp Creek:

  • Streamflow: Swamp Creek (56b)
  • Temperature: Swamp Creek at Bothell Way (56A) and Swamp Creek at Locust Road bridge at river mile (RM) 5 (56C)

Stream Sediment

Sediment data were collected from Swamp Creek as part of the Stream Sediment Monitoring Program starting in 1987. Data were compiled for the years 1987 through 2002. Data analysis identified no significant trends for any of the parameters tested.

A basin-wide sampling effort took place in 2007, including eleven sites along the reach of Swamp Creek. At least one chemical was above Sediment Cleanup Objectives (SCO) at each site, suggesting uncertain effects to sediment-dwelling animals. Nickel concentrations exceeded the SCO at every site. Arsenic concentrations exceeded the SCO at sites AA470 and VV470 and chromium at site AA470. Concentrations of bis(2-ethylhexyl)phthalate (an ubiquitous chemical found in many plastic consumer products) exceeded the SCO at sites 0470, AB470, CD470, XX470 and ZZ470. The concentration of total PCB Aroclors exceeded the SCO at site VV470 and the concentration of dieldrin (an organochlorine pesticide) exceeded the SCO at site XX470. Additional data were collected (acid volatile sulfide/simultaneously extracted metals ratio) that suggest metals were available only at sites F470 and II470.

The presence of PCBs and dieldrin in the sediments at VV470 and XX470, respectively, is troubling because production of these chemicals in the United States ceased in the 1970s. These types of chemicals are persistent in the environment and can also bio-magnify in the food chain and show up at elevated levels in fish that live in both in this creek and in Lake Washington.

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 Swamp Creek, please visit the Puget Sound Stream Benthos webpage.

Special Studies

Habitat Inventory and Assessment of Three Sammamish River Tributaries: North, Swamp and Bear Creeks

From August to November 1999, King County conducted habitat assessment on North, Swamp, and Little Bear Creek (King County WLRD, May 2001). These streams are the three major northern tributaries to the Sammamish River. The Swamp Creek habitat assessment took place from the mouth of the creek to 380 meters north of 164th Street SE in Snohomish County.

The results of the habitat assessments indicate that the channel and habitat structure of a number of the segments in all three streams are frequently degraded relative to values from published "properly functioning conditions" for the Puget Sound or the Pacific Northwest region. These data provide important baseline information for any restoration projects that might occur in the basins, as well as for monitoring changes in habitat quality. This study may be used for a limiting factor analysis for the threatened chinook salmon as well as other salmonid species in these basins.

Small Streams Toxicity/Pesticide Study

In 1999, King County conducted a pesticide study on Lyon, Juanita, and Lewis Creeks. In 2000, the study was repeated at the same locations. In 2001, Big Bear and Issaquah Creeks were sampled. And in 2002, North, Little Bear, and the 124th street Creeks were sampled. Rock Creek was tested for pesticides in 1999 and then it was used as the reference stream for toxicity testing during each year of the study. The County collected samples for pesticides, other organics, metals, suspended solids, and toxicity (Ceriodaphnia dubia, and Selenastrum capricornutum).

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.