Stream Insect Health

About this environmental indicator
King County monitors stream health by collecting samples of benthic macroinvertebrates, commonly referred to as "bugs," from selected streams.

Scientists use a scorecard system called the Benthic Index of Biotic Integrity (B-IBI) to rank the health of streams. The scores are based on the types of stream bugs living in the stream and the number of different kinds of stream bugs present. By using this scoring system, we can compare very different streams to each other and rank their ecological health.

Status: The 2003 data are the most recent available. A total of 128 stations in 55 streams within 15 subbasins across the Lake Washington/Cedar/Sammamish watershed (WRIA 8) and the Green/Duwamish watershed (WRIA 9) were sampled. Results for unincorporated and incorporated areas within King County are dramatically different. In 2003, 31 percent of the sampled streams in unincorporated areas had benthic insect communities in good or excellent condition, whereas none of the stream stations in incorporated areas rated this high.

Influencing factors: Development, pollutant runoff, loss of forest cover, stream and wetland ecological health, elevated stream temperatures, fish migration barriers, and of invasive and non-native plants are a few factors that can have an affect on the stream insect populations. Insufficient flows in streams can reduce number of sampling sites, affecting annual comparisons.

Existing DNRP response: WLR continues to implement programs focusing on minimizing degradation from development and pollutant runoff from farms, preventing the loss of forest cover and its numerous stormwater benefits, or implementing watershed improvement projects. King County's Stormwater Program focuses on flow control to minimize adverse effects from development, provides surface water design standards for new development and inspects and maintains stormwater control facilities.

The county continues to work with landowners to restore streamside parcels that have important benefits as aquatic resources. In addition, WLR's capital projects program builds small and large stream and wetland enhancement projects. Basin stewards work with the local community to respond to resident's inquiries for watershed protection, coordinate efforts among diverse public agencies, facilitate watershed project implementation, provide assistance to monitoring programs and provide public education opportunities. The Agriculture Program works with farmers and livestock owners to prevent agricultural pollutants from running off into streams.

Priority new actions: Implementation of the county's Critical Areas Ordinance and federal total maximum daily load (TMDL) requirements for impaired water bodies are regulations that will also support water quality improvements in both incorporated and unincorporated areas.

Data from 2005 are currently being analyzed. The taxonomic analysis of the 2006 samples will be complete in summer of 2007.

Stream Insect Health
Findings from B-IBI 2003
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