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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 USGS 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 (BB474) located at Carter Road. Sampling at this site was discontinued in 2008 due to budget cutbacks. 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 at various streams in King County. (Click here for information about Special Studies involving Swamp Creek.)


Water Shed Image Swamp Creek originates in the Paine Field and West Casino Road area of South Everett. 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 percent of the drainage is impervious and 19 percent forested cover. The drainage basin includes Scriber Lake, Martha Lake, and Lake Stickney and drains portions 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 recent habitat survey (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.

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.


Since 1997 volunteers with the Salmon Watcher Program have been recording salmon observations at various locations in Swamp Creek. Volunteers have consistently seen coho in the creek. Less commonly spotted are kokanee and sockeye salmon. Observers have not seen chinook salmon.

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, 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. Swamp Creek is now categorized as “Core Summer Salmonid Habitat” for aquatic life use and “Extraordinary 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 September 15th through May 15th. Swamp Creek is on the 2012 Washington Department of Ecology’s (Ecology) 303(d) list for violation of dissolved oxygen, pH and temperature standards (Category 5). See Table 1 for a summary of water quality violations in the creek during the most recent water year.

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. Dissolved oxygen 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, visit the Water Quality Index page.

Table 1. Routine monitoring summary statistics for this station from 1971 to 2018
ParameterNumber of SamplesMeanMinimumMaxmiumMedianStandard Deviation
Dissolved Oxygen (mg/L)2599.86.713.99.91.6
Temperature (°C)38510.
Turbidity (NTU)3543.270.2022.002.522.45
Conductivity (mSIEMS/cm)230182.899.1241.0183.032.0
Total Suspended Solids (mg/L)3895.330.5052.003.606.34
Ortho-Phosphorus (mg/L)3890.02700.00730.07900.02600.0103
Total Phosphorus (mg/L)3890.05490.00670.19700.05200.0203
Ammonia (mg/L)3890.02370.00560.12000.02100.0138
Nitrate (mg/L)3890.77770.18802.32000.71000.3483
Total Nitrogen (mg/L)3121.05410.38902.90000.99250.3393
Fecal Coliform(CFU/100ML)38829385600160585

Table 2. Storm water monitoring summary statistics for this station from 1971 to 2018
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 gauges: Swamp Creek located on north-east side of creek underneath bridge near Burke-Gilman trail at RM 0.44 ( 56A), and Swamp Creek located on north-west side of creek west of Locust Rd. bridge at RM 5 (56C) and one streamflow gauge: Swamp Creek (56b) on Swamp Creek.

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 (AVS/SEM 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 web page. To see the benthic macroinvertebrate data for Swamp Creek, please visit the Puget Sound Benthos webpage.

Special Studies

Habitat Inventory and Assessment

From August to November 1999, King County conducted habitat assessment on North, Swamp, and Little Bear creeks (King County WLRD, May 2001). These streams are the major three 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 S.E. in Snohomish County. Click here to download the Habitat Inventory and Assessment for North, Swamp, and Bear Creeks (PDF format).

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 Lyon, Swamp, and Little Bear creeks. 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). For more information, visit the pesticide study Web site.

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. Visit the WRIA 8 Web page to see how this creek is part of this WRIA 8 planning process.