Idylwood Creek Site A620

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King County Water Quality Monitoring

King County monitors the ecological health of Idylwood Creek in a variety of ways including collecting and analyzing water, sediment, and benthic invertebrate samples. Since 1995 water quality samples have been collected monthly at Station A620 located at the footbridge in Idylwood Park. Sediment samples have been collected from Idylwood Creek as part of the Streams Sediment Monitoring Program starting in 1987. Benthic invertebrates were sampled from the creek in 2002 and 2003.

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

Idylwood Creek Watershed

The Idylwood Creek watershed is located at the northwest end of Lake Sammamish in the City of Redmond. Headwaters of the creek originate in the City of Bellevue. The creek drains into Lake Sammamish roughly 50 feet north of the swimming beach area in Idylwood Park.

Volunteers with the Salmon Watcher Program have been making observations at various locations within the Idylwood Creek basin since 2000. No fish were observed in Idylwood Creek during the 2004 observation period (King County WLRD April 2005).

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. Idylwood Creek is considered a Class AA water body under the 1997 rules. As the 2003 rules become effective Idylwood Creek is categorized as “Salmonid Spawning, Rearing, and Migration Habitat” for aquatic life use, and “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 and fecal coliform bacteria standards. See Table 1 for a summary of water quality violations in the creek during the most recent water year.

To view charts of current water quality conditions in the creek, please visit the links at the top of the page.

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 Idylwood Creek is rated either “high” or “moderate concern”. Low dissolved oxygen and high fecal coliform bacteria compromise water quality in Idylwood Creek. To see how Idylwood Creek ratings compare with other stream sites, visit the Water Quality Index page.

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

 

Stream Sediment

Sediment data were collected from Idylwood 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 during data analysis for any of the parameters tested. Results indicate that Idylwood Creek sediments exceeded on sediment quality guideline (nickel). Of the 27 streams monitored in King County, Idylwood Creek had the 7th lowest metals concentrations.

Benthic Invertebrates

In both 2002 and 2003, benthic invertebrate samples were collected, analyzed, and benthic invertebrate index scores (BIBI) were calculated for Idylwood Creek. Benthic invertebrates are an important link in the food chain for fish in the creek and are an excellent indicator of stream health.

BIBI scores from both years indicate that conditions in Idylwood Creek were very poor for benthic invertebrates. About 95 percent of the species identified were tolerant of degraded conditions. 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

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 page to see how Idylwood Creek is part of this WRIA 8 planning process.