Dan Nyquist has spent his entire life on a farmstead on the shore of Smith Lake in southwestern Wright County. Smith Lake went dry due to drought in the 1930s. Nyquist was just a young boy when the moisture came back and the lake started to fill up again. His parents sent him and his siblings to the lake to trap muskrats and other furbearers to earn extra money. "The muskrats, mink, ducks, geese, and other wildlife that returned were unbelievable," Nyquist said.
But by the late 1970s, Smith Lake had changed. Nyquist called it "the dead sea." The once clear waters with lush aquatic plants and plentiful wildlife had become turbid, overcome with algae, and dominated by carp and black bullheads. The lake attracted little wildlife.
Smith Lake is one of 4,000 shallow lakes statewide. These waters—15 feet or less in depth and covering 50 acres or more—make up about one-third of Minnesota's 11,842 lakes. While all lakes support wildlife in some way, shallow lakes provide the most wildlife habitat per acre. Beds of rooted aquatic vegetation thrive in clear, shallow lakes because sunlight penetrates to the bottom. Aquatic plants and invertebrates provide both food and shelter for wildlife, including ducks, geese, swans, grebes, terns, minks, beavers, and otters.
Unfortunately, two-thirds of the shallow lakes in the prairie-farmland region of the state are turbid. They have been degraded by decades of increased nutrient runoff and changes in fish communities. Extensive agricultural drainage has dramatically changed watersheds, eliminating most wetlands and increasing connections between the remaining wetlands, lakes, and rivers. These connections provide a ready pathway for undesirable nutrients and fish.
Help is on the way for these struggling waters. The Department of Natural Resources developed the statewide Shallow Lakes Program in 1985 to help area wildlife managers enhance shallow lakes for waterfowl and other wildlife. The Clean Water, Land and Legacy Amendment's Outdoor Heritage Fund has supported the acceleration of shallow-lake projects around the state.
For Smith Lake, the program has been a lifesaver.
Like Smith, many shallow lakes would have historically gone dry during extended droughts. But such droughts don't seem to happen very often, and when they do, today's increased runoff dampens the effect. An effective way to mimic a drought and bring back clear water and wildlife habitat in these lakes is to slowly draw down water levels. These drawdowns may partially or totally drain a lake for a few weeks, months, or more than a year. Then the lake is gradually refilled.
A drawdown works like a reset button for a shallow lake: It transforms a lake back to a clear-water condition. Sediments in shallow lakes can be very loose and mucky, and a drawdown gives them a chance to dry out and harden, making them less likely to be stirred up by waves or carp. This, in turn, stimulates plant growth. A drawdown is often necessary to rid a lake of harmful fish.
Emptying a lake, even temporarily, is a very dramatic event—yet dramatic actions can often have dramatic results. A properly timed drawdown and reflooding could transform Dan Nyquist's "dead sea" to crystalline water and a rich diversity of aquatic plants. When aquatic vegetation and associated invertebrates return, so does a vibrant community of wetland wildlife.
Aquatic invertebrates range from microscopic crustaceans like Daphnia, also known as water fleas, to macroinvertebrates like scuds, crustaceans that can reach an inch long. These invertebrates are a rich source of food for numerous aquatic and terrestrial wildlife species, from blue-winged teal to least sandpipers to leopard frogs. A lake that contains droves of Daphnia is often called "duck soup" because it is a divine feast for waterfowl.
In shallow lakes, a series of interactions occurs among Daphnia, aquatic plants, and fish like black bullheads and carp. The interactions help determine if the water will be clear or turbid. Daphnia feed by filtering algae from the water. When abundant, they can filter the entire volume of a shallow lake in a day, helping clear algae out of the water. Then beneficial rooted aquatic plants can thrive, keeping soils on the lake bottom in place. They also provide food for wildlife and shelter for Daphnia and other invertebrates.
If fish become too abundant, they can eat all the Daphnia, causing algae to explode in abundance and turn the water green and thick like pea soup. In addition, bottom-feeding rough fish such as common carp can stir up sediments while uprooting aquatic plants, causing the water to become more turbid and releasing nutrients that stimulate additional algae growth. In turbid conditions, rooted aquatic plants don't receive enough light to grow. When aquatic plants are gone, shallow lake sediments are left exposed and easily stirred up by waves, further decreasing water clarity. This is the state that Smith Lake was in when the Shallow Lakes Program came to the rescue.
Management of Smith Lake started when an ideal spot for a type of fish barrier called a "high-velocity tube" was located downstream from the lake. A high-velocity tube is simply a long culvert placed at a slope to create a strong current of water that fish cannot overcome.
Because Smith Lake has a maximum depth of 5.8 feet, it historically often winterkilled fish when oxygen became depleted under the ice. Due to a series of mild winters after the installation of the fish barrier, Smith Lake failed to winterkill. The lack of a natural winterkill triggered the decision to do a drawdown to eliminate carp and black bullheads and improve water clarity.
Before Smith Lake could be drawn down, many steps had to be completed. First, to decide if a drawdown was feasible, the DNR worked with Ducks Unlimited on an engineering study to determine how much water could be removed from Smith Lake. Ideally, all the water is drained from a lake during a drawdown, but sometimes the topography around a lake limits the amount of water that can be removed. In the case of Smith Lake, Ducks Unlimited found a nearly full drawdown was possible.
Next, the DNR drafted a management plan and presented it to the public for input. With public support, the DNR in 2009 designated Smith Lake as one of Minnesota's 49 wildlife management lakes, giving the agency legal authority to manage water levels.
Dennis Larson, owner of the land at the lake's outlet, granted the DNR an easement to build a water-level control structure on his property. Ducks Unlimited's Living Lakes Initiative funded the structure and engineering through the Outdoor Heritage Fund. The structure was finished in late February 2011, and the drawdown began that summer.
A drawdown can be compared to a bathtub with the drain plug open. The water in the bathtub flows out, and any new water coming in also flows through the tub and out the drain. So goes a drawdown—the control structure is opened, and water flows to an outlet stream. The progress of the drawdown depends on how much water comes in from the contributing watershed and the capacity of the lake's outlet to send it downstream.
Smith Lake was an empty bathtub the summer and fall of 2011. The lake bottom became exposed mud flats, providing excellent habitat for shorebirds that poke through the mud to find invertebrates to eat. The number of birds attracted local birders, who spotted rare species including red knot and piping plover.
Ending the drawdown is like filling the bathtub again. The tub can be filled only if the tap is turned on when the drain is plugged. The tap for a lake is the inlet or inlets from its contributing watershed. How fast a lake is refilled depends on the size of the watershed, how much rain falls, how much water the landscape around the lake absorbs, how many inlets are coming into the lake, and the water level set by the water control structure. The level is usually increased gradually to minimize damage to newly established aquatic vegetation.
The Smith Lake drawdown lasted a year, which allowed the sediments to consolidate, killed carp and black bullheads, and established more aquatic vegetation. The dead fish on the shore in 2012 didn't last long. According to Nyquist, "Vultures and eagles had them cleaned up in about a month." The water became gin clear with several species of vegetation. The Daphnia in the lake exploded so abundantly that clouds of them could be seen from a boat. Duck soup was once again on Smith Lake's menu, and waterfowl eagerly responded. This past spring, at least eight waterfowl species were spotted after ice-out, several species of frogs created a loud chorus, and trappers found plenty of muskrats.
Future drawdowns will be necessary to maintain good habitat conditions in Smith Lake. Shallow lakes specialists will monitor water clarity and vegetation distribution to determine when more management is needed. The goal is to keep fish abundance low. Test netting conducted in 2013 detected no fish.
According to DNR area wildlife manager Fred Bengtson, "The success of returning Smith Lake to a healthy shallow lake, teeming with wildlife, is nothing short of astonishing and could only have been accomplished with the cooperation and encouragement of lakeshore landowners, hunters, wildlife enthusiasts, conservation agencies, and organizations like Ducks Unlimited. With Legacy funding, we have greatly expanded opportunities to manage more shallow lakes in Minnesota."
Landowners Dan Nyquist and Dennis Larson couldn't be happier. Duck hunting is excellent, and muskrats have returned. Looking back, Larson said he was skeptical of the drawdown in the beginning. "A guy isn't used to change. I wondered if it was worth doing all this and if it would work," he said. "Now that it's done, it was definitely worth it."