Skip to main content

Benthic Macroinvertebrate Monitoring

Benthic Macroinvertebrate Monitoring

King County, Washington


King County uses a variety of tools to monitor stream health throughout the county. This monitoring  is done to track trends in water and habitat quality that may affect the bountiful natural resources and recreational opportunities found across our region. 

One of the best ways to monitor stream health is by collecting and analyzing the benthic macroinvertebrates that reside in streams. These organisms are commonly referred to as “stream bugs". (You can find links to other tools King County uses to monitor stream health in the right-hand 'Related Information' menu on this page).

Benthic [ben·​thic] (adj.): of, relating to, or occurring at the bottom of a body of water

Macroinvertebrate [mac·​ro·​in·​ver·​te·​brate] (n.): animals lacking a spinal column that are visible with the naked eye

Specifically, scientists collect samples of macroinvertebrates that live in and on the bottom of the streambed. The samples are then analyzed by identifying and counting the different types (taxa) of macroinvertebrates present. We monitor these because they are good indicators of water quality, habitat conditions, and overall stream health. Some examples of benthic macroinvertebrates include mayfly larvae, caddisfly larvae, stonefly larvae, crayfish, worms, snails, and mussels. 

Scientists use information from these samples and a scoring system called the Puget Lowlands Benthic Index of Biotic Integrity (B-IBI) to characterize stream health. B-IBI scores are based on the number and type of macroinvertebrates found in the stream samples. These scores are used to classify stream sites into five categories: Excellent, Good, Fair, Poor, or Very Poor. Streams that support many different types of macroinvertebrates, including ones that are sensitive to poor water quality and degraded habitats, are considered excellent. Streams with only types that can tolerate degraded conditions are considered very poor. 

King County's Benthic Macroinvertebrate Ambient Monitoring Program has been collecting benthic macroinvertebrate samples since 1994. Currently, we annually collect samples from over 170 sites. All of King County's B-IBI data can be viewed on the Puget Sound Stream Benthos website, which is where over 20 agencies and jurisdictions also store and share regional B-IBI data.

-->>>View King County's B-IBI data.<<---

For questions about information on this page, please contact Jenée Colton, Lead, Toxicology and Contaminant Assessment Group or Kate Macneale, Environmental Scientist.