Forbes Creek Site 0456

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King County Water Quality Monitoring

King County monitors the ecological health of Forbes Creek in a variety of ways including collecting and analyzing water, sediment, and benthic invertebrate samples. Since 1979 water quality samples have been collected monthly near the mouth of the creek at Station 0456 located near the end of the pump access road on NE 106th Street. Sediment samples have been collected from Forbes Creek as part of the Streams Sediment Monitoring Program starting in 1987. Benthic invertebrates were sampled from the creek in 2002 and 2003.p>

From time to time special studies have been conducted at various streams in King County. Special studies on Forbes Creek are listed at the bottom of this page.

Forbes Creek Watershed

The Forbes Creek basin comprises approximately 1000 acres. The creek originates at an elevation of 240 feet above sea level and flows roughly 1.8 miles thorough the City of Kirkland and a wetland area before entering the north east corner of Lake Washington. Land use in the basin is primarily mixed residential (WSDOT 2003).

Fisheries

Little is known about the existing fish population in Forbes Creek. The creek historically supported cutthroat trout and coho salmon have been introduced (Metro 1990). Volunteers with the Salmon Watcher Program have made observations at river mile 0.2 and at river mile 0.9. Only one coho was observed in the creek in 2001 (King County, 2002).

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. Forbes Creek is considered a Class AA water body under the 1997 rules. As the 2003 rules become effective Forbes 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 dissolved oxygen, temperature, and fecal coliform bacteria standards. See Table 1 for a summary of water quality violations in the creek during the most recent water year.

Forbes Creek has historically had low dissolved oxygen concentrations and high temperatures (Metro 1990). Because the monitoring station is located near a large wetland with slow moving water and high levels of organic matter, low dissolved oxygen and higher temperatures are not surprising.

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

Long-term Trends

A 25-year (1979 – 2004) trend analysis was conduced with baseflow data collected from Forbes Creek. This analysis showed some improvements in the water quality since 1979. Ortho-phosphorus, total nitrogen, nitrates, and fecal coliform bacteria have all shown a significant decrease over this 25-year time period. However, stream temperatures and conductivity have increased, and dissolved oxygen concentrations have decreased significantly during this same time period.

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 Forbes Creek was rated “high concern” primarily due to high nutrients, high fecal coliform bacteria, and low dissolved oxygen concentrations. To see how Forbes Creek ratings compare with other stream sites, visit the Water Quality Index Web page.

For more information about long-term trends in other streams or to view charts of current water quality conditions in Forbes 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 a water temperature gauge on Forbes Creek (20a).

Stream Sediment

Sediment samples were collected from three stations approximately a mile apart, along a three miles reach of Forbes Creek in the summer of 2005 (see Map). Concentrations of bis(2-ethylhexyl)phthalate (a chemical found in some plastics) and zinc in samples from stations 0456 and XX456 were above levels likely to cause adverse effects in sediment-dwelling animals. Other chemicals, including metals and dieldrin (an organochlorine pesticide) were also present at levels suggesting that adverse effects are uncertain. Additional data were collected (AVS/SEM ratio) at these sites to better understand the toxicity potential of metals. This information indicates metals are not likely bioavailable at 0456. However at station XX456, metals are bioavailable and may cause adverse effects.

The presence of dieldrin in the sediments at 0456 is troubling because production of this pesticide ceased in the 1970s. This type of pesticide (like DDT) is persistent in the environment and can also bio-magnify in the food chain and show up at elevated levels in fish that live in both in this creek and in Lake Washington. There is currently a fish advisory that suggests limiting the consumption of some fish from Lake Washington due to high levels of some contaminants.

At station XX456, sediments consisted primarily of gravel, indicating that this site is very dynamic and chemicals found there have not been there very long and will quickly wash downstream. The presence of arsenic, zinc, nickel and bis(2-ethylhexyl)phthalate at this site indicate that an on-going upstream source of these contaminants. These results are surprising because XX456 is located in a residential neighborhood just downstream of Forbes Lake.

Benthic Invertebrates

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

Scores from both years indicated that conditions in Forbes Creek for benthic invertebrates were very poor. Data from both years indicated that a high percentage of the invertebrates (greater than 75%) were tolerant of degraded conditions. Very few individuals of species sensitive to degraded conditions were present and only one individual that is long lived was collected at the site during 2002 and 2003. Longer-lived species tend to take longer to reproduce and also are among the first to disappear when a streams ecosystem is altered by human activity such as urbanization.

Special Studies

In October of 2002 about 50 4th grade students from Alexander Graham Bell Elementary School collected water samples from several sites within Forbes Creek (and Juanita Creek). The students then studied the water quality constituents. This project was made possible through the creative thinking of 4th Grade teachers at Alexander Graham Bell, and a partnership with the City of Kirkland. The Department of Public Works Storm/Surface Water Division provided the water quality testing kits used by the students. This project was partially funded by a King County Waterworks Grant.

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 Forbes Creek is part of this WRIA 8 planning process.