Lewis Creek Site A617

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King County Water Quality Monitoring

King County monitors the ecological health of Lewis 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 near the mouth of the creek at Station A617 located at a bridge near the intersection of 187th Ave SE and 185th Pl. SE. Sediment samples have been collected from Lewis Creek as part of the Streams Sediment Monitoring Program starting in 1987.

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

Lewis Creek Watershed

The mainstem of Lewis Creek is a relatively short, 1.5 miles, with numerous branched tributaries (Kerwin 2001). The mainstem originates in a low gradient area above the Eastgate region of Bellevue on the northeast side of Cougar Mountain. The creek then flows through a steep, wooded ravine before entering another low gradient reach downstream of Interstate 90 and where it drains into the southern end of Lake Sammamish.

The basin encompasses 1,209 acres. The dominant land use in the Lewis Creek basin is single family residential and rural residential (Kerwin 2001). In 2000, it was determined that approximately 28 percent of the basin was impervious surfaces.

Fisheries

Numerous fisheries studies have been done on Lewis Creek (The Watershed Company 1988, 1989; URS Corp., 1987; King County, 1995; Ostergaard, 1998; King County 2000c). A culvert located at river mile 0.75 at Interstate 90 is a barrier to fish migration. Below this barrier, in the lower reaches of the creek, kokanee, sockeye, coho and cutthroat trout were observed during a recent habitat and barrier assessment done by the Washington Department of Fish and Wildlife (WDFW, 2000). King County staff and volunteer salmon watchers have also observed adult coho, sockeye, kokanee, and chinook in the last seven years (King County 2000c, 2001b, 2001c, June 2002). A fish habitat and population assessment conducted in 1992 by the Watershed Company noted the presence of cutthroat trout, steelhead trout, kokanee, and coho (Kerwin 2001).

Beginning in 1997, volunteers with the Salmon Watcher Program have made observations in Lewis Creek. Kokanee salmon have been observed in the creek. Less commonly seen are coho, sockeye, and chum salmon.

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. Lewis Creek is considered a Class AA water body under the 1997 rules. As the 2003 rules become effective the creek is categorized as “Core Summer Salmonid 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 DO, FC, and temperature standards. See Table 1 for a summary of water quality violations in the creek during the most recent water year.

Studies conducted as part of the Lakemont Development process found exceedences of State water quality criteria for lead, zinc, and fecal coliform bacteria (Herrera 1995).

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. In 2000-01 and 2001-02 Lewis creek was rated “moderate” concern. During the last four water years Lewis Creek was rated “high concern” primarily due to high fecal coliform bacteria and high nutrient concentrations. To see how these 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:

 

Hydrology

King County maintains a streamflow gauge: Lewis Creek at West Lake Sammamish Parkway SE (63a) and a precipitation gauge: Lewis Creek Rain Gauge (63u) on Lewis Creek.

Stream Sediment

Sediment data were collected from Lewis 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 Lewis Creek sediments did not exceed any sediment quality guidelines. Of the 27 streams monitored in King County, Lewis Creek had the 3rd lowest metals concentration.

Special Studies

Lakemont Boulevard

Public concern over the 1998 construction of Lakemont Boulevard in the sensitive Lewis Creek corridor led to major environmental controls. Bellevue and King County staff worked together to control stormwater road runoff. Several reports have been written in relation to this project including:

• The Watershed Company has conducted several studies on Lewis Creek as part of the Lakemont Division Four project (Watershed Company 1988, 1989, 1992).
• Lewis Creek: General Site Survey and Level II Stream Survey, Final Report. June 1994. Dames and Moore, Inc.
• Final Project Report: Lewis Creek Monitoring Program, May 1995. Herrera Environmental Consultants.

Small Streams Toxicity/Pesticide Study

As part of King County’s Small Streams Toxicity/Pesticide Study, pesticide concentrations and toxicity were measured in Lewis Creek in 1999 and 2000. 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.

Habitat Assessment

Washington Department of Fish and Wildlife conducted a fish barrier evaluation and habitat assessment on Lewis Creek in 2000.