How’s the water? Let’s ask the fish and bugs
What fish can tell us about the health of lakes and streams.
Did you know the fish and bugs, or biological communities, living within Minnesota’s rivers and streams can tell a story about the quality of the water and habitat within them?
Each year, the MPCA’s Biological Monitoring Unit samples biological communities from about 200 to 400 sites on rivers, streams, and ditches throughout Minnesota. These waterways range in size from a few feet wide to large main-stem waterways, such as the Mississippi or Minnesota river. So, how are the biological communities sampled this past summer, and what can they tell us?
Fish are sampled once per site from June through September, using electrofishing methods where an electric current is placed into the water, temporarily stunning any fish within range of the current. MPCA crews use a net to collect the fish, regardless of size, from the smallest minnows to the largest game fish, and then place them into a tub of water. Fish are separated by species, and counted, measured, weighed, then released back into the stream. Depending on stream width and depth, a variety of electrofishing methods are used to maximize sample efficiency and quality. For small streams, a sampler walks through a stream carrying a shocker wand and backpack that houses a battery. For large rivers, samplers use boats with shocking equipment attached.