10/02/2026
Something we've been asked before: why do we collect stream insects to measure water quality instead of just testing the water?
Fall sampling season is underway, and the Volunteer Stream Monitoring Program groups are out running events right now, so it's a good time to get into some of the reasoning behind MiCorps' methodology.
Testing the stream works, but it only captures the moment you take the sample. An hour later, or after a rainstorm, for example, the readings can change. If something polluted the stream a month ago and washed through, a test today might not pick it up.
The insects represent a longer snapshot. For example, mayflies, stoneflies, and caddisflies live in a stream for months, and each kind can only survive in certain conditions. The pollution-sensitive ones can start to diminish when water quality drops and don't return until it recovers. So the insects we find reflect what conditions have been like across the whole season, not just the day we sampled.
A single water test in a moving stream tells you about that moment. The insects are closer to an ongoing record of the stream 🙂
Here is the current list of VSMP events happening across the state: https://www.michigan.gov/egle/about/organization/water-resources/glwarm/micorps/monitoring-events
