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King County Water Quality Monitoring

King County monitors the ecological health of Springbrook Creek in a variety of ways, including collecting and analyzing water, sediment, and benthic invertebrate samples. Water quality samples have been collected from Springbrook Creek since 1977. Station 0317 is located near the mouth of the creek at the bridge. Beginning in 1987, sediment quality samples have been collected from Springbrook Creek. King County began collecting benthic macroinvertebrate samples in Springbrook Creek in 2002.

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


Water Shed Image The Springbrook Creek watershed is located in South King County in Water Resource Inventory (WRIA) 9 in and around the Cities of Kent and Renton, Washington. The mainstem of the creek flows for 12.0 miles, with an additional 19.1 miles of tributaries. Springbrook Creek becomes the Black River at a point 0.65 miles upstream of the Green River. The Creek, via the Black River, enters the Lower Green River at River Mile (RM) 11.0 (Kerwin and Nelson, 2000; Herrera, 2005).

Historically, the Black River drained Lake Washington, combining with the Cedar River and Springbrook Creek before its confluence with the Green River to become the Duwamish River. Since the construction of the Lake Washington Ship Canal in 1916, the Black River receives very little drainage besides flows from Springbrook Creek (Kerwin and Nelson, 2000, Herrera, 2005).

The Springbrook basin drains an area of 15,763 acres and has two distinct physical settings. The eastern half of the basin has steep rolling hills rising to elevations about 525 feet above the valley floor. The western half of the basin is virtually flat. Panther Lake and some smaller ponds and wetlands are located in the eastern half. Panther Creek and Mill Creek (not to be confused with Mill-Hill Creek also in WRIA 9) are the major tributaries to Springbrook Creek. Panther Creek drains Panther Lake and enters into Springbrook Creek at RM 1.3. Mill Creek is located entirely in the Green River valley and enters Springbrook Creek at RM 3.8 (Kerwin and Nelson, 2000; Herrera, 2005).

Total land use in the Springbrook Creek basin is almost entirely of low to high-intensity development. Forest and agriculture are less than 10% of the basin while the remaining land use consists of scrub, wetlands, and other (barren land, grassland, and open water). 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% 90% 6% <1% 2% <1%

For more information about the Springbrook Creek watershed, please visit the WRIA 9 website for the Lower Green River Subwatershed.


Coho salmon, cutthroat trout, and winter steelhead adults have been observed spawning in Springbrook Creek and its tributaries (Kerwin and Nelson, 2000). Resident and anadromous cutthroat have been observed throughout the basin. As summarized in the 2000 WRIA 9 Habitat Limiting Factors and Reconnaissance Assessment Report, there was roughly 17.9 miles of potential fish habitat within the Springbrook basin with 17.2 miles of this accessible to anadromous salmonids.

The Lower Green River Baseline Habitat Survey Report provides more detailed information about habitat conditions in the Springbrook Creek area.

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.

State water quality standards were revised in 2003. Springbrook Creek is now categorized as “Spawning, Rearing and Migration Habitat” for aquatic life use and “Primary Contact” for recreational use. As part of the updated water quality standards, portions of Springbrook Creek have been assigned an additional “Supplemental Spawning and Incubation Protection” temperature criteria of 17.5 °C. The creek is on the Washington State Department of Ecology’s (Ecology) 303(d) list for violation of DO, FC bacteria, and bioassessment standards (Category 5). The creek has an EPA-approved Green River Temperature Watershed total maximum daily load (TMDL) plan in place and implemented for FC bacteria (Category 4a).

A water quality data assessment conducted for the Green-Duwamish River in 2003 found that when evaluating most water quality parameters, conditions at Springbrook Creek (A317) were poor relative to the Soos Creek and Newaukum Creek stations (Herrera, 2005). Total iron concentrations exceeded the Washington State chronic criterion in one baseflow sample. The herbicide 2,4-D was detected in two baseflow samples, while polycyclic aromatic hydrocarbons were detected infrequently at Springbrook Creek.

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 baseflow water quality data collected from Springbrook Creek. This analysis shows that there has been changes in water quality during that 28 year time period that indicate some decline in water quality. Total nitrogen concentrations have increased and and DO concentrations have decreased significantly. The pH values showed that the creek has become significantly more acidic though values are still within acceptable range of 6.5 to 8.5. Some improvements in water quality in Springbrook Creek were also observed in the 28-year trend analysis. Total suspended solids, turbidity, ortho-phosphorus, total phosphorus, ammonia, nitrate, and FC bacteria have all decreased significantly.

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

Table 1. Routine monitoring summary statistics for this station from 1977 to 2024
ParameterNumber of SamplesMeanMinimumMaxmiumMedianStandard Deviation
Dissolved Oxygen (mg/L)3425.51.312.75.52.0
Temperature (°C)48111.30.920.411.14.1
Turbidity (NTU)44515.241.40170.0013.3011.26
Conductivity (mSIEMS/cm)312273.167.0604.0291.089.5
Total Suspended Solids (mg/L)48112.131.80354.007.2025.28
Ortho-Phosphorus (mg/L)4810.06450.00700.90000.04740.0788
Total Phosphorus (mg/L)4810.16770.01211.80000.14700.1139
Ammonia (mg/L)4820.21810.01200.83400.18800.1390
Nitrate (mg/L)4810.47230.14501.13000.46000.1538
Total Nitrogen (mg/L)3930.96980.12101.74000.97300.2207
Fecal Coliform(CFU/100ML)4465677145001501236

Table 2. Storm water monitoring summary statistics for this station from 1977 to 2024
ParameterNumber of SamplesMeanMinimumMaxmiumMedianStandard Deviation
Dissolved Oxygen (mg/L)447.
Temperature (°C)6110.
Turbidity (NTU)5318.564.4359.0015.6011.70
Conductivity (mSIEMS/cm)32126.243.9301.0107.064.5
Total Suspended Solids (mg/L)6130.644.00100.0025.0022.41
Ortho-Phosphorus (mg/L)610.03390.00720.11900.03000.0218
Total Phosphorus (mg/L)610.15390.02440.41500.14400.0782
Ammonia (mg/L)610.11350.01200.40200.08710.0824
Nitrate (mg/L)610.39430.18200.79500.35200.1443
Total Nitrogen (mg/L)590.90010.21601.96000.84800.2689
Fecal Coliform(CFU/100ML)6121305340009004535


King County operates a stream gage on Springbrook Creek: Springbrook Creek at SW 43rd Street southwest of the City of Renton, Washington (03G). The U.S. Geological Survey (USGS) also operates a stream gage further upstream near 84th Ave South (12113346).

Stream Sediment

Sediment data were collected from Springbrook Creek as part of the Stream Sediment Monitoring Program starting in 1987. Data were compiled and analyzed for the years 1987 through 2012. Data analysis identified no significant trends for any of the parameters tested.

Sampling of the legacy site, 0440, continued through 2012, with basin wide sampling occurring in 2008. Results for 2008 sampling indicate that sediment in the Springbrook Creek basin exceeded the Sediment Cleanup Objective (SCO) for arsenic and cadmium at sites 0317, K317, L317 and M317. Nickel concentrations exceeded the SCO at M317 and N317. Concentrations of bis(2-ethylhexyl)phthalate exceeded the SCO at K317, L317, M317 and N317. Total PCB Aroclor concentrations exceeded the SCO at M317. AVS/SEM ratios suggested that metals were not bioavailable at 0317, L317 and N317 meaning adverse effects to benthic animals are unlikely at these sites.

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

Special Studies

Pyrethroid Survey of King County Stream Sediments 2014 Final Report

Pyrethroids are a group of synthetic insecticides commonly used in residential areas. Residential and commercial use has resulted in an increased detection in urban runoff, which can be harmful to aquatic life. In October 2014, a pyrethroid survey was conducted in sediments collected from six King County streams. These streams include: Juanita, Forbes, Thornton, Pipers, Springbrook, and Mill Creeks. Results found that bifenthrin was the only pyrethroid detected in the sediment samples; and most detected concentrations were below the reporting detection limit. Percent finds and TOC content, which varied substantially by creek, may be influencing bifenthrin detections. These results suggest that sediments may contain toxic levels of pyrethroids even if they are not detectable above detection limits in this study.

Green-Duwamish Water Quality Assessment

In 2001, King County initiated a separate comprehensive study of the Green-Duwamish Watershed, called the Green-Duwamish Watershed Water Quality Assessment (GDWQA). Several reports evaluate data collected as part of the GDWQA. Springbrook Creek is included in this analysis.