One way to determine water quality is to do clarity monitoring (Secchi depth) and chemical testing (phosphorus) in the lake. Another way to determine water quality is to look for clean water indicators. Using both water quality monitoring and clean water indicators is a good way to fully understand your lake’s health and ecosystem. In science, two explanations that come to the same conclusion are better than one.
Clean water indicators are plants and animals that live in and around the lake and rely on it for survival. Organisms reflect their environment and live there year round (in some form). Some animals are very tolerant to pollution, while others are very intolerant. Clean water indicators are the animals that are intolerant to pollution. If your lake never had these indicators, don’t worry, it could be that they never lived there. The indicators mentioned below mainly apply to lakes over 50 feet deep in northern and north-central Minnesota. If you used to have these indicators and you don’t have them any more, that’s when you’ll know that water quality has been impacted in some way.
Hexagenia mayfly
These mayflies are filter feeders found in the soft silt or sand of streams and lakes. Because mayflies can’t survive in water that lacks oxygen, they are good indicators of the amount of eutrophication (phosphorus). These mayflies are everywhere during one week in June and then they’re gone. They all emerge as adults at the same time to increase their chance of mating successfully.
Common Loon
Loons are diving birds that use their eyesight to capture their food. They need clear water and healthy fish populations. Also, in order to make nests and protect their young, they need undisturbed natural shoreline with tall vegetation. If your lake is ringed by manicured lawns, you may lose your loons due to lack of nesting areas.
Tullibee/Cisco
Tullibee/Cisco are important forage species for the lake’s game fish. They are mainly found in lakes over 60 feet deep, and they need highly oxygenated water to live. When lakes lose their Tullibee populations, it can indicate increased eutrophication. The loss of Tullibee then affects game fish populations because they are a major food source. To find out if your lake has Tullibee, visit the DNR Lakefinder web site: http://www.dnr.state.mn.us/lakefind/index.html. Look up your lake by name and county, and when your lake information comes up, click on “go” under the heading “Lake Information”. This page will show the DNR Fisheries report for your lake.
Freshwater Mussels
Mussels filter oxygen and particles from the water, cleansing the water in the process and absorbing what they consume into their bodies and shells. It is for these reasons that mussels are sensitive to changes in their environment and serve as indicators of the health of our lakes and streams.
Degradation of our lakes and rivers from runoff of silt and chemicals as well as physical changes from damming, channelization, and dredging, have taken their toll on native mussels in North America. In addition, invasive zebra mussels can out-compete native mussels and displace them from their native areas.
In summary, fish, birds and other aquatic organisms need a healthy habitat to survive. To maintain a healthy lake ecosystem, this habitat needs to be preserved. If these clean water indicator species disappear from your lake, it could indicate a water quality problem. Decreases in water quality and the loss of habitat and spawning sites for game species are often the primary mechanisms that create opportunities for “less popular” fish species (bullhead, carp). The best way to avoid this is to protect habitat where game fish spawn and rear their young. Also, to protect fish and bird food sources such as invertebrates, aquatic insects, and aquatic plants.
Until next week, enjoy the lakes!