Yarrow Creek Site A499

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King County Water Quality Monitoring

Since 1976, King County has been conducting monthly ambient water quality monitoring at one site at the mouth of Yarrow Creek. Station A499 is located at the mouth of the creek near the intersection of Points Drive and Lake Washington Blvd, 25 feet downstream from the culvert.

Yarrow Creek Watershed

The Yarrow Creek basin comprises approximately 640 acres. The creek originates in the Bridle Trails State Park at an elevation of 400 feet and flows 2.95 miles before entering Lake Washington along the northeastern shoreline. Yarrow Creek is placed in Ecology’s Noncore Salmon/Trout Aquatic Use Category which sets criterion for the protection of spawning, core rearing, and migration of salmon and trout, and other associated aquatic life.

Land use in the basin includes Bridle Trail State Park, a business complex, condominiums, single family residences, and a portion of State Route 520 (Metro 1990). Although the water quality in the creek was rated “good overall” in 1989, impacts common to developing watershed were observed. It was noted that much of the stream had been piped to accommodate development.

Fisheries

The suitability of Yarrow Creek for salmonids was rated “good” in 1989 (Metro 1990). The benthic invertebrate population was rated “fair,” as it was dominated by small mayflies and earthworms. Lack of spawning substrate was stated to be the primary limiting factor for salmonids. In addition, migratory fish passage is blocked on Yarrow Creek at river mile 0.2 at the culvert under NE Points Drive (Kerwin 2002).

Little is known about the existing fish population in Yarrow Creek. The creek historically supported coho salmon (Kerwin 2002). Kokanee were presumed to use Yarrow Creek based on historical records of a Native American village located near its mouth. Volunteers with the Salmon Watcher Program have been making observations at river mile 0.3 (1998, 1999, 2000, 2001) and at river mile 0.5 (1997, 2001). Only one unidentified fish was observed in the creek in 2000 and 2001.

Water Quality

The water quality in Yarrow Creek was characterized as “good” in 1989 (Metro 1990). The creek was determined to have relatively high temperatures (though none exceeded state criteria), high pH, and high nitrates. See Table 1 for a summary of water quality violations in the creek during the most recent water year.

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