Stream Bugs 

Stream Monitoring

Every summer, Stream Team volunteers stir things up looking for “stream bugs”. These critters, otherwise known as benthic macroinvertebrates, provide valuable information about water quality and the biological health of streams. They are also fun to collect and examine.

After all the samples are gathered, they are sent to a lab where they are assessed according to a Benthic Index of Biological Integrity (BIBI). This index gives a biological health rating for our streams (low, medium or high biological integrity), as well as other important information regarding what may be impacting the health of our streams. Currently, Stream Team volunteers gather samples from twenty streams throughout Thurston County.

Gathering benthic macroinvertebrate samples gives volunteers a chance to get their feet (boots) wet while enjoying stream habitat and collecting valuable stream health data!

What are benthic macroinvertebrates?

Benthic macroinvertebrates are critters that do not have a backbone and live part or all of their lives in the bottom of streams. They can include snails, aquatic worms and arachnids, clams, crustaceans (like crayfish and shrimp), and insects. Some are tolerant of pollution or habitat disturbance in the stream, and some are sensitive to pollution and habitat disturbance.

“Stream bugs” are excellent indicators of stream health because:

  • they are relatively sedentary (therefore they cannot easily swim away from pollution);
  • they exhibit tolerance or intolerance to impacts to streams; and
  • they are fairly easy to collect.

If you go: What to Expect

Before going out to gather the samples, volunteers attend a weekday evening training (held two separate times in mid-late June or early July). During the training, volunteers learn how and why stream bugs are used to assess stream health, as well as the monitoring protocol.

Volunteers can choose to monitor one or more sites. Each monitoring site is led by a trained staff person. On average, it takes about 3 to 5 hours to gather the samples and prepare them to be mailed off to a lab. A variety of monitoring dates and times are offered during the weekday, in the evenings, or on weekends to accommodate people’s busy schedules.

Monitoring sites vary in accessibility: a few sites require climbing down steep terrain and/or climbing over downed trees. Volunteers help carry equipment to the monitoring location. Waterproof boots or sandals are recommended. Sunscreen or insect repellent may be useful for some sites.

For more information, including questions about monitoring locations and accessibility, contact Ann Marie Pearce at or
360-754-3355 ext. 6857.

Sign me up!

BIBI Scores

Monitoring Sites