Water Quality: Bugs Tell a Story

Each spring, the Estuary Program and our volunteers collect data about the condition of the creek and samples of macroinvertebrates or “macros”, which are insects, snails, and other creatures that are visible to the naked eye.

How Do We Monitor?

What Do the Bugs Tell Us?

Some macros are very sensitive to pollution, so if you find them in your creek, you know that the water is free of pollution and has cold, clean water. The caddisfly, pictured here, builds a small structure around itself which serves as its house. These creatures are sensitive to pollution. In creeks with poor water quality, pollution-sensitive species such as caddisflies are rarely found.

The macros we collect spend a portion of their life cycle in the creek. Eggs hatch and the larvae spend an extended period of time (up to a few years for some species) in this juvenile life stage. They eventually emerge from the water as adults to mate and lay eggs, usually in or near the water. We capture the macros in their larval stage.

What Does the Data Show?

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Based on the types of macros found in a sample, the lab provides a score for each site. The map above shows the averaged scores with data through 2015. Those colored green have high scores, which means the creeks have cold clear water with lots of oxygen and good habitat that supports healthy bug and fish populations. Those coded yellow and orange have fair and poor bug scores and might not be hospitable habitats for sensitive species such as steelhead.

We thank the Harold J. Miossi Charitable Trust for their generous support of this bioassessment survey effort over the years.