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King County Water Quality Monitoring

King County monitors the ecological health of the creeks on Vashon-Maury Island. Monthly water quality sampling on Vashon Island began in November 2006 at the seven stations listed below. Currently, sampling continues at Fisher, Gorsuch, Judd, Mileta, Shinglemill, and Tahlequah.

Christensen Creek - Station VA23A is located upstream of the mouth on private property just south of Lisabuela Park. Christensen Pond forms the headwaters of Christensen Creek, which flows into Colvos Passage. Sampled from 2006 - 2007.

Fisher Creek - Station VA41A is located just upstream of the Vashon HWY SW crossing between Shawnee RD and 115th Ave SW. Fisher Creek drains into the western shore of Quartermaster Harbor. Sampled from 2006 - 2012 and resumed in 2014.

Gorsuch Creek - Station VA65A is located just upstream of the mouth on private property at the end of SW Gorsuch Rd on the northeast end of Vashon Island. Sampled from 2006 - 2008 and resumed in 2013.

Judd Creek - Station VA42A is located upstream of the mouth at the SW 225th St crossing on private property. Judd Creek empties into the northwest end of Quartermaster Harbor. Sampled from 2006 - 2008 and resumed in 2013.

Mileta Creek - Station VA45A is located near the mouth, downstream of Dockton Rd SW just north of the intersection with 75th Ave SW. Mileta Creek empties into the northeast end Quartermaster Harbor. Sampled from 2006 - 2012 and resumed in 2014.

Shinglemill Creek - Station VA12A is located just downstream of the SW Cedarhurst Rd crossing. Shinglemill Creek flows from Fisher Pond on the north side of Bank Road to where it empties into Fern Cove on the northwest corner of Vashon. Sampled from 2006 - 2012 and resumed in 2014.

Tahlequah Creek - Station VA37A is located just upstream of the SW Pohl Rd crossing near the Talequah Ferry Terminal. Sampled from 2006 - 2007 and resumed in 2014.

From time to time, additional studies have been conducted on Vashon-Maury Island. Click here for more information about Special Studies.


Water Shed Image

Vashon-Maury Island encompasses approximately 37 square miles of which 29.7 square miles are on Vashon Island and 7.0 square miles on Maury Island. The two islands are linked by an arrow isthmus and are therefore not truly independent islands. Vashon-Maury Island is bordered on the west by Colvos Passage from the Kitsap Peninsula, on the south by Dalco Passage from Tacoma, on the East by Puget Sound and King County, and on the north by Puget Sound. Vashon Island is about 13 miles long (north to south) and 4 miles across (east to west) in the widest areas. Maury Island is about 5 miles long (northeast to southwest) and about 1 mile across (northwest to southeast).

The topography of Vashon-Maury Island varies from sea level to elevations in excess of 460 feet based on U.S. Geological Survey topographic maps. New LiDAR (Light Detecting And Ranging) data has improved the accuracy of the surface topography data. The maximum elevation on the Island is just over 500 feet at Maury Island Marine Park. The shoreline extent of Vashon-Maury Island is just over 58 miles, most of which lies beneath steep, slide-prone slopes. The Island has numerous (>70) stream basins and two of these are larger with subbasins, Judd Creek and Shinglemill Creek. All of these stream basins drain into Puget Sound.

All of Vashon-Maury Island is designated as rural and is therefore outside the Urban Growth Boundary (UGB). Low-density residential development covers much of the Island with zoning of one home per five and ten acres. Higher density residential areas are concentrated in the Vashon Town Center, Vashon Heights, Burton, Dockton, and along parts of the shoreline. Multifamily, commercial, and industrial uses are presently concentrated in the unincorporated town of Vashon and adjacent areas where sewer and other urban services are available. The predominant land use for this basin is forest, followed by some development and not much agriculture. Forest in the basin is mostly mixed forest with considerable amounts of deciduous and evergreen. Developed lands are mostly open space and agriculture is only pasture/hay agriculture. There is some scrub and other land uses (grassland), but no wetlands. See Table 1 below for more details on land use.

Table 1. Total land use in the basin

Agriculture Developed Forest Scrub Other
Total 1% 12% 77% 3% 7%

The percentage of forested land is ~73% when compiled into three broad categories of forest, non-forest and developed land. The other two categories, non-forest and developed land, have percentages of 16% and 11% respectively (King County, 2005).


With funding from the Vashon/Maury Island Audubon Society, the Trout and Salmon Foundation, the General Service Foundation, and King County Department of Natural Resources and Parks, Wildfish Conservancy (previously known as Washington Trout) performed a comprehensive water-typing survey on Vashon Island in 2000 and 2001. The purpose of the survey was to ensure that the trout and salmon streams receive the maximum legal protections available in the face of growing development (Washington Trout, 2001 ). During the survey Washington Trout found direct evidence of coho salmon in at least two streams, Shinglemill Creek and Baldwin Creek. They also found substantial use by sea-run cutthroat trout throughout the island's streams. Washington Department of Fish and Wildlife records indicate that coho and chum salmon (O. keta) have historically used several other island streams. Volunteers with the Salmon Watcher Program have reported seeing coho and chum salmon, and cutthroat trout in both Fisher and Judd creeks.

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. Vashon-Maury Island creeks are now categorized as "Core Summer Salmonid Habitat" for aquatic life use and "Extraordinary Contact" for recreational use because these streams are tributaries to extraordinary quality marine waters (WAC 173-201A-610 through 173-201A-612 ). As part of the updated water quality standards, portions of the creeks have been assigned an additional “Supplemental Spawning and Incubation Protection” temperature criteria of 16 °C. Several creeks are listed on the Washington State Department of Ecology's (Ecology) 303(d) list for violations of water quality standards (Category 5):

  • Fisher: water temperature
  • Judd: bioassessment and water temperature
  • Shinglemill: bioassessment

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.

Water Quality Index

A Water Quality Index (WQI) rating system was developed by Ecology that evaluates several water quality parameters and gives and overall rating of “high,” “moderate,” or “low” concern. To view WQI scores for the stations located on Vashon Island, visit the Water Quality Index webpage.

Table 1. Routine monitoring summary statistics for this station from 2006 to 2020
ParameterNumber of SamplesMeanMinimumMaxmiumMedianStandard Deviation
Dissolved Oxygen (mg/L)1559.42.713.010.02.5
Temperature (°C)1559.41.715.69.72.8
Turbidity (NTU)1535.220.5841.504.365.26
Conductivity (mSIEMS/cm)155113.557.4184.0108.030.2
Total Suspended Solids (mg/L)1545.600.5093.402.4011.20
Ortho-Phosphorus (mg/L)1540.01230.00210.41800.00740.0342
Total Phosphorus (mg/L)1530.03160.00970.56000.02330.0462
Ammonia (mg/L)1540.02910.00322.30000.00760.2092
Nitrate (mg/L)1542.36830.10708.82001.43501.9734
Total Nitrogen (mg/L)1532.73250.48809.18001.77002.0941
Fecal Coliform(CFU/100ML)1511071450022404


King County maintains numerous stream, precipitation, and crest/staff gages on Vashon-Maury Island (this list only includes gages for the streams listed above):

  • Streamflow: Shingle Mill Creek (43a), Judd Creek (28a), Fisher Creek at mouth (65B), and Tahlequah Creek at mouth (65A)
  • Precipitation: Judd Creek (28u), West Judd Creek (28Y), and Tahlequah Creek (65U)
  • Crest/staff: Christensen Creek (VA23) and Gorsuch Creek (VA65)

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). Several sites on Vashon-Maury Island were sampled for benthic invertebrates in 2001.

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, please visit the Puget Sound Stream Benthos webpage.

Special Studies

Vashon-Maury Island Water Resources Evaluation (WRE)

The Vashon-Maury Island WRE was a 2004 - 2010 project designed to describe and assess the water resources of the Vashon-Maury Island, which is a part of the Central Puget Sound Watershed. The project provided a better understanding of how different activities adversely affect the island's water quality and quantity and led to an updated, more accurate water supply budget for the island.