The Washington Conservation District has been fielding a lot of questions lately from people concerned about plants like lily and duckweed growing in their lakes. Their typical response runs something along the lines of, “Well, yes. Plants do grow in lakes.” Now, I admit that I myself have been guilty of under-appreciating aquatic plants, ahem… macrophytes, a time or two. Last summer, for example, I hoped to swim across the lake at my friend’s cabin up north until I dove in, became hopelessly tangled in weeds, panicked, and then frantically clawed my way out of the water as the deep, mucky soil along the shoreline threatened to swallow me whole. A ninety-five degree day at the lake is a lot less fun when the water’s only there for scenery. That said, the common desire to have a sandy, weed-free lakeshore with clear, deep water does not really line up with the reality of what most of our Minnesota lakes have to offer. Furthermore, when people start removing aquatic plants in an attempt to manipulate their lakes, the unforeseen consequences usually outweigh the benefits.
While we may consider aquatic plants to be a nuisance, they are actually the building blocks for life in lake, stream and river systems. They produce life-giving oxygen for fish and provide food and shelter for a range of birds, mammals, reptiles, amphibians and fish. Any angler can tell you that the best fishing spots are typically near aquatic plant beds where the fish can spawn, find food and hide from predators.
Dozens of different reptiles, amphibians and birds call the water’s edge home, including a few that are in danger of extinction. The threatened Blanding’s turtle can be found in deep and shallow marshes, shallow bays of lakes, and impoundments where there are dense patches of plants both in the water and along the shoreline. They are omnivores, eating crayfish, snails, tadpoles, fish, insects, worms, grasses, and berries. Boreal chorus frogs call from within grassy clumps in the water and are nearly impossible to find even when you can hear them. Mink frogs are shoreline-dependent but also forage on and around floating mats of vegetation away from the shore. Even the lowly mudpuppy salamander, host to the endangered salamander mussel, is dependent on aquatic plants to find the worms, fish and other small amphibians that they eat.
When humans begin removing shoreline habitat in search of a weed-free lakeshore, the turtles, frogs and birds are some of the first to disappear. Soon thereafter, the fish swim off in search of better spawning sites and more to eat as well. Ironically, however, the so-called rough fish like bullheads and carp are better equipped to survive in these newly plant-free habitats. As more and more shoreline aquatic plants are removed around a lake, then, the wildlife structure often changes from one with walleye, bass, Blanding’s turtles, frogs, herons and egrets to one with carp, bullheads and a whole lot of geese.
In addition to providing wildlife food and habitat, aquatic plants actually help to keep lake water cleaner too. The plants act as a filtering system, helping to clarify the water by absorbing nutrients like phosphorus and nitrogen that could stimulate algal blooms. Plant beds also stabilize soft lake and river bottoms and reduce shoreline erosion by softening the effect of waves and current. The role of rooted aquatic plants is especially important in shallow lakes, which tend to exist in one of two states, either clear water with plants or green, algae-filled water with no plants.
Of course, not all aquatic plants are created equally. Blue green algae, for example, are more like bacteria than plants. They aren’t a good food source for other living things in the food chain and can cause dangerous algae blooms in lakes and rivers that have too much phosphorus in the water. There are also a number of non-native, invasive plants like Eurasian watermilfoil that can make lake life miserable for boaters and swimmers. Maintaining healthy native aquatic plant communities can actually help prevent the establishment of these invasive non-native plants, however, in addition to keeping blue-green algae under control.
Some common macrophyte “friends” you might find in your community lakes include water lily, American pondweed, duckweed, stonewort, coontail, bladderwort, and bulrush. White water lily attracts birds and is eaten by waterfowl and mammals. Duckweed is an important high protein source of food for waterfowl and is actually eaten by people in some parts of Asia. Yellow pond-lily provides food and shelter for many fish and underwater insects and stonewort is particularly good for ducks. All of these plants are just as much a part of Minnesota lakes as our state fish the walleye, and our state bird the loon.
The best source for information about aquatic plants in Minnesota is the Department of Natural Resources website (once it is up and running again). If you are interested in restoring native plants along your shoreline, visit www.BlueThumb.org for plant recommendations and helpful guidelines. If you’re craving a day on a nice sandy beach, check out one of the Washington County Parks such as Square Lake Park in May Township, or Big Marine Park in Scandia or Lake Elmo Regional Park. There are also several good city beaches, including Lily Lake in Stillwater, Lake St. Croix Beach on the St. Croix River and Silver Lake Park in North St. Paul.