Issaquah Creek Site 0631

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King County Water Quality Monitoring

Since 1976, King County has been conducting monthly baseline water quality monitoring in Issaquah Creek at three sites. Station 0631 is located near the mouth of the creek at the bridge on SE 56th, east of Lake Sammamish State Park. Station A632 is located near the mouth of the North Fork on E Lake Sammamish Parkway SE. And Station A631 is located on the mainstem upstream of the state fish hatchery, 30 feet upstream from the bridge on W Underwood Blvd.

From time to time special studies have been conducted at various streams in King County. Click here for information about Special Studies of Issaquah Creek.

Issaquah Creek Watershed

The Issaquah Creek Basin is one of the three most significant basins in urbanizing King County. The upper and middle Issaquah Creek Basin is identified as a Regionally Significant Resource Area because of its exceptional fisheries habitat and undeveloped character (Kerwin, 2001). Carry and Holder creeks in the upper basin provide particularly excellent habitats for salmonids.

Issaquah Creek headwaters originate from the steep slopes of Cougar, Squak, Tiger and Taylor mountains. The basin encompasses about 61 square miles and includes Holder, Carey, Fifteen-mile, and McDonald creeks as tributaries to Issaquah Creek.

More than 75 percent of the basin is forested, with the remainder in wetlands, pastures, and less than 10 percent urban and cleared areas (Kerwin, 2001; King County 1996). As of 2001, 30 percent of the basin is zoned forest production, 12 percent is within the urban growth boundary, and the remaining 58 percent is zoned rural. Over 40 percent of the land is in public ownership with Washington Department of Natural Resources, Washington State Parks, King County Parks, and City of Issaquah Parks. The population in the basin is projected to increase by 18 percent by 2020.

Fisheries

Eight species of salmonids (six anadromous) are known to utilize the Issaquah Basin. The Issaquah Creek Hatchery at river mile (RM) 3.0 currently produces chinook, coho, and Lake Washington steelhead. All fish not used for production are allowed to spawn in the natural habitat of the creek (Kerwin, 2001). An early-run kokanee stock is also present in Issaquah Creek.

Volunteers with the Salmon Watcher Program have been making observations within the Issaquah Creek basin since 1997. Chinook, coho, and sockeye salmon have been observed in the creek. Cutthroat trout and kokanee salmon are also observed, but less commonly seen. In 2001 volunteers began making observations in Holder Creek. For more information about fisheries in the Issaquah Subarea visit the Issaquah Creek Subarea Web page.

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 bacteria (FC). 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. Issaquah Creek was designated a “Class A” water body under the 1997 rules. As the 2003 rules become effective Issaquah Creek and headwaters are categorized as “Core Summer Salmonid Habitat” for aquatic life use, with the exception of Holder Creek, which is designated as “Char Spawning and Rearing Habitat”. As part of the updated water quality standards, Issaquah Creek has been assigned an additional “Supplemental Spawning and Incubation Protection” temperature criteria of 13 ºC to be applied from September 15th through June 15th. The creek is designated as “Primary Contact” for recreational use. The creek is on the 2004 Washington Department of Ecology’s (Ecology) 303(d) list for violation of dissolved oxygen criteria. See Table 1 for a summary of water quality violations in the creek during the most recent water year.

Long-term Trends

A 25-year (1979 – 2004) trend analysis was conducted with baseflow water quality data showed some significant changes in the water quality since 1979. Improvements in water quality at the mouth of the creek (0631) are evident by a significant decrease in ortho-phosphorus, nitrate, and total nitrogen. Near the mouth of the North Fork (A632) there was a significant decrease in ortho-phosphorus, total phosphorus, nitrate, total nitrogen, turbidity, total suspended solids, and fecal coliform bacteria. However, there was a significant increase in ammonia at station A632 during this same time period. At the upstream station (A631) nitrates and total nitrogen concentrations decreased significantly, but there were significant increases in ortho-phosphorus and total phosphorus and a significant decrease in dissolved oxygen. All three stations showed a significant increase in water temperatures and conductivity.

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. During the last six water years the station at the mouth of the creek (0631) and the upstream station (A631) have been rated “low” to “moderate” concern primarily due to high fecal coliform bacteria and high nutrients. The North Fork station (A632) has been rated “moderate” concern due to high fecal coliform bacteria, nutrients, and low summer dissolved oxygen concentrations. To see how the WQI ratings at Issaquah Creek stations compare with other stream sites, visit: the WQI page.

For more information about long-term trends in other streams or to view charts of current water quality conditions in Issaquah Creek, please visit the links at the top of the page.

A review of the 2008 data shows the following violations of State water quality standards:

 

Hydrology

King County maintains two streamflow gauges on Issaquah Creek: North Fork Issaquah Creek (46a) and North Fork Issaquah Creek in Grand Ridge (46t) and one water temperature gauge: Issaquah Creek at SE 56th Street (25A) .

Stream Sediment

Sediment data were collected from Issaquah Creek as part of the Stream Monitoring Program starting in 1987. Data were compiled and analyzed for the years 1987 through 2002. Data were analyzed for trends, correlations, and were compared to sediment quality guidelines. No significant trends were identified for any of the parameters tested and Issaquah Creek sediments did not exceed any sediment quality guidelines. Of the 27 streams monitored in King County, Issaquah Creek had the 16th highest metals concentrations.

Benthic Invertebrates

The County also monitors stream health by collecting samples of benthic invertebrates from selected streams as part of King County's Benthic Invertebrate Program. Benthic invertebrates are an important link in the food chain for fish in the creek and are an excellent indicator of stream health. In 2003, a benthic invertebrate sample was collected, analyzed, and a benthic invertebrate index score (BIBI) was calculated from a site in lower Issaquah Creek, just upstream of Sammamish Road in the city of Issaquah.

The BIBI score from this site indicates that conditions in Issaquah Creek were poor for benthic invertebrates. The sample was dominated by species that are tolerant to degraded conditions. Also, very few individuals of species that are long-lived or sensitive to degraded conditions were present. Longer-lived species tend to take longer to reproduce and along with sensitive species are among the first to disappear when a stream ecosystem is altered by human activity such as urbanization.

Special Studies

Volunteer

The City of Issaquah partnered with volunteers to restore parts of Issaquah Creek. The main activity was removing invasive vegetation and replacing it with shading vegetation. School teachers are adopting sections of the creek and including stewardship in their curriculum. This project was partially funded by a King County Waterworks Grant.

Small Streams Toxicity/Pesticide Study

As part of King County’s Small Streams Toxicity/Pesticide Study, pesticide concentrations and toxicity were measured in Issaquah Creek in 2001. The County collected samples for analysis of pesticides, other organics, metals, suspended solids, and toxicity (Ceriodaphnia dubia, and Selenastrum capricornutum). For more information, visit the pesticide study web site.

Issaquah Creek Basin Planning

Numerous studies have been conducted in conjunction with basin planning and salmon conservation efforts. For more information about work in the Issaquah Creek Subarea please visit the Issaquah Creek Subarea Web page.

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 for future generations. Visit the WRIA 8 Web page to see how Issaquah Creek is part of this WRIA 8 planning process.

Issaquah Creek Valley Groundwater Management Area

King County is partnering with the City of Issaquah and Sammamish Plateau Water and Sewer District in these Groundwater Activities (2005-2007) within ICV GWMA:

• Hydrogeologic mapping within the Issaquah Creek Basin
• Exempt Well Assessment
• Groundwater Model of Upper Issaquah Creek Basin

For more information about this groundwater management program visit the Issquah Creek Valley Ground Water Management Area program Web site