Health of shallow lakes slowly improving, but more work needed
Deeper, glacial lakes like Green Lake in Spicer get most of the attention from anglers during the fishing season, but at least early, the shallower prairie lakes draw anglers itching to catch fish.
Shallower lakes warm up faster than larger lakes, meaning increased fish activity.
But our smaller lakes are also more susceptible to influences that degrade the water quality and the fishing experience, which has become an increased concern for property owners on these lakes, others who frequently use these waters and those whose job it is to manage these resources.
Nicole Hansel-Welch, a shallow lakes specialist with the Minnesota Department of Natural Resources in Brainerd, wrote in an email that non-native fish species, external nutrient loading and development are threats to the health of shallow lakes in Minnesota.
"Carp are an issue on most shallow lakes in the southern half of the state," she noted. "They increase internal nutrient cycling in a lake, causing turbidity which leads to loss of aquatic vegetation that provides food and habitat for waterfowl, wildlife and other fish species."
Nutrient loads factor greatly in the quality of water in any lake, stream or river. The more runoff from agricultural lands that flow into a lake, the greater the load of excessive nutrients in the water.
"(It) also leads to a loss of water clarity and aquatic plants, reducing the overall health of a shallow lake and reducing quality habitat," Hansel-Welch wrote.
Development harms the shoreline of lakes and hurts the aquatic vegetation, she noted.
"Shoreline development can impact areas of shoreline habitat and can change the amount of surface use on lakes and increase demands for management that is not consistent with the nature of shallow lakes (i.e. deep, weedless areas for swimming)," Hansel-Welch wrote. "Increased boating can be damaging to aquatic plants and disruptive to staging and breeding waterfowl. Development can be done in a way to reduce/minimize impacts, though. People are also becoming more aware of how shallow lakes are different than deeper lakes and appreciating them for what they are."
Limiting or reducing the human impact on shallow lakes takes a lot of work. Methods can be met with resistance. Aeration -- artificially creating oxygen in the water -- keeps fish and aquatic vegetation alive during the winter when they would otherwise die.
Without aeration, a number of area lakes -- Foot Lake in Willmar and Lake Wakanda included -- would have many years where a majority of fish in those lakes would die, affecting the fishing experience for years to come.
"We can still hope to do some manipulations of the fish populations without the additional aid of aerations," said Bruce Gilbertson, the manager for the DNR's Fisheries office in Spicer. "Like Lake Minnetaga, a relatively shallow prairie lake, but does not have significant winterkill. At Lake Elizabeth, the oxygen level got low enough that the aeration system was used to prevent winterkill. We're looking at the various types of aeration systems that don't have to be turned on every year. For many of the lakes that we have, the oxygen levels are going to decline to a point where some of our game fish would be lost."
Reducing external nutrient loads, wrote Hansel-Welch, takes cooperation with landowners in the surrounding watershed.
"... wetlands and grasslands can be restored in the watersheds of these lakes, best management practices like buffer strips and low-till/no-till could be implemented. Best management practices can be applied for storm water management."
It may still be a long road ahead for our shallow lakes. But there is some reason for hope.
"Over the last 20 years, we have seen a shift where, especially bullheads, there's been a reduction of their abundance on a majority of our lakes, including the shallow prairie lakes," Gilbertson said.
"It's not like it's all doom and gloom, but we're a long way from having the problem solved."