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.
Bugs, or macroinvertebrates, are sampled once from August through September at the same locations where fish are sampled. A specialized net is used to take 20 individual samples from the most dominant habitat types: rocky areas, instream vegetation, undercut banks, woody debris, and/or and piles of leaves in the stream. The macroinvertebrates are placed in a jar with alcohol to preserve the sample and brought to a laboratory for identification.
Fish and macroinvertebrates are a great indicator of stream health because some species are sensitive to disturbances. This sensitivity allows biologists to assess where issues may exist based on the communities present. For example, some fish are very tolerant of low dissolved oxygen levels while others are extremely sensitive to low dissolved oxygen levels. Looking at biological samples, habitat assessments, and water chemistry samples can provide a good picture of the stream health. Examples of potential problems may include low dissolved oxygen, high sediment concentrations, agricultural or industrial runoff, or lack of habitat. The information gathered can guide watershed partners to restoration or protection efforts.