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. (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.
Chinook, coho, and sockeye have been observed at almost all sites in Issaquah Creek by volunteer salmon watchers, including the uppermost site at RM 8.9 (King County, 2002). Trout and kokanee have also been observed. 2001 was the first year that volunteers recorded any species in Holder Creek. For more information about fisheries in the Issaquah Subarea visit the Issaquah Creek Subarea Web page.
Water Quality
The Washington State Department of Ecology revised its water quality standards in 2003, but not all of the revised standards have been approved by the U.S. Environmental Protection Agency (EPA). Issaquah Creek is considered a “Class A” water body under the 1997 rules and will be designated “Salmon and Trout Non-core Migration and Rearing Habitat” as the 2003 rules are approved. The creek is on the 2004 Washington Department of Ecology’s (Ecology) 303(d) list for violation of dissolved oxygen criteria.
A review of the 2005 water quality charts show that water quality conditions at the mouth of the creek (0631) were good with the exception of four violations of State fecal coliform bacteria criteria. At the upstream station (A631) there were two violations of State fecal coliform criteria. In addition, nutrients and total suspended solids were relatively high at station A631 in May. Water samples from the North Fork station (A632) violated State temperature criteria in July and August, and dissolved oxygen criteria and fecal coliform standards in May and October. Nutrient concentrations were relatively high (TP in May, August, October and TN in May and August) at the North Fork station and total suspended solids were very high in October.
A 25-year (1979 – 2004) trend analysis (baseflow 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 was a significant increase in ortho-phosphorus and total phosphorus and a significant decrease in dissolved oxygen. All three stations showed significant increase in water temperatures and conductivity.
A Water Quality Index (WQI) rating system was developed by the State Department of Ecology that evaluates several water quality parameters and gives and overall rating of “high,” “moderate,” or “low” concern. 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.
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) .
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.
Macroinvertebrates
Macroinvertebrate Program. Based on invertebrate data collected in 2002 and 2003, water quality at the mouth of Issaquah Creek (0631) was characterized as “fair - poor” while the upstream station (A631) was characterized as “fair”. For more information about this program visit King County's Benthic Macroinvertebrate Web page.
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.
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