Willmert Lake (Main Bay)

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We have an topograpical map for online viewing near the top of this page. Lake-Link Pro users can download an print a topograpical map of Willmert Lake (Main Bay) (.pdf format) along with 2,700 more lake maps. For more information on all the benefits of Lake-Link Pro click here.

Wilmert Lake

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Wilmert Lake is a 362-acre lake located 5 miles south of the city of Fairmont in Martin County. Wilmert Lake has a maximum depth of 8.0 feet and is managed primarily for northern pike and secondarily for walleye and yellow perch. The Wilmert Lake outlet flows into Amber Lake through Mud Lake. Amber Lake is part of a chain of Lakes known as the "Fairmont Chain" that supports a diverse fish community. High water levels connect these lakes frequently and fish movement throughout the "Fairmont Chain" of lakes is common. The substrate in Wilmert Lake is dominated by a layer of muck over a base of sand and gravel. Some areas of rubble can be found near the shoreline and are most likely from field stone that was dumped into the lake after it was removed from area farm fields and/or wave action. A full fish and aquatic vegetation survey was conducted during the week of August 6th, 2010.

Wilmert Lake is particularly susceptible to low dissolved oxygen levels in the winter, which then leads to pocket winterkills of fish. Over the last 40 years, Wilmert Lake has experienced 12 documented winterkills with the last major winterkill during the winter of 2000-2001. After that severe winterkill in 2000-01, a vegetation and fish survey was conducted. Seven different species of aquatic vegetation were present and made fish and vegetation sampling extremely difficult as the lake was fully covered with the vegetation. Fish known to reduce submergent vegetation such as adult common carp, adult black bullhead, and adult bigmouth buffalo were rare or not present during sampling of 2000-01. During the current 2010 survey, the vegetation has nearly disappeared and the undesired fish (adult carp and adult bigmouth buffalo) have returned. Only one species of aquatic vegetation is present (river bulrush). It is apparent that connection to Amber Lake and the Fairmont Chain is adequate enough when water levels are high (as they have been regularly since the last major winterkill in 2000-2001) to allow fish movement as indicated by the return of common carp, and bigmouth buffalo. Other species caught during the 2010 survey were black bullhead, black crappie, bluegill, fathead minnow, freshwater drum, golden shiner, northern pike, orangespotted sunfish, spotfin shiner, walleye, white crappie, white sucker and yellow perch indicating that other more desirable species are also utilizing the connection from Amber Lake.

The northern pike catch rate in 2010 was 0.2 fish/trap net, only 2 fish were caught. The two pike caught were 37 and 39 inches. The abundance of northern pike was low and smaller northern pike were absent from the sample. To increase the abundance of northern pike in Wilmert Lake fish were stocked in the spring of 2010. No northern pike from the spring 2010 stocking were found in the summer 2010 survey which may indicate significant predation by other species of fish. Also, it may be that the fish emigrated to the other "Fairmont Chain" lakes. Habitat in Wilmert Lake may need to improve to sustain a population of northern pike at an acceptable abundance.

The walleye catch rate during 2010 was 11.0 fish/gill net, which is within the expected range for this type of lake (2.3 to 18.1 fish/gill net) and greater than the long-term average catch rate of 8.0 fish/gill net. The trap net catch rate was 10.4 fish/trap net, which is 3 times the expected range (3.0 fish/trap net). With a trap net catch rate as high as was observed and a gill net catch rate within the interquartile range, it appears that the walleye abundance in Wilmert Lake is high. Although walleye abundance may be high, the average length of walleye in Wilmert Lake was only 10 inches with a range of 8 to 21 inches. The walleye population was dominated by smaller fish. Approximately 80% of the walleye sampled were from the 2008 year class which corresponds to a year in which 364,000 walleye fry were stocked. The walleye population was bordering between fair and poor condition indicating foraging stress. Many times a population of fish that is dominated by a single year class will have a low condition indice. This is most likely due to competition for limited forage resources. As mortality increases and the abundance of the 2008 year class decreases, the overall condition will likely improve.

The yellow perch catch rate in 2010 was 83.0 fish/gill net, which is more than 3 times the expected range for this type of lake (25.0 fish/gill net) and 1.5 times the long-term average of 55.9 fish/gillnet for Wilmert Lake. The average length was 7 inches with a range of 5 to 8.5 inches. The size structure of the yellow perch indicated a population that is dominated by smaller fish. The population is dominated by two year classes, one year old (5 to 6 inches) and two year old (7 to 8 inches) yellow perch. The overall condition was good and indicates that the yellow perch population is foraging successfully. As the two strong year classes mature in 2011 and 2012 the population size structure will increase and become more balanced.

The black crappie catch rate was the highest ever observed in the trap net with a catch rate of 61.8 fish/net. This catch rate is 3 times the expected range for this type of lake (20.5 fish/trap net) indicating a population that is abundant. The average length of black crappie was 8.5 inches with a range of 4 to 10.5 inches. Approximately 97% of the black crappie sampled was greater than 7.5 inches. The size structure of black crappie indicated a population that is dominated by fish in the 8 to 10 inch size range. The overall condition of the population was good and indicates they are foraging successfully. During 2011 and 2012, if winterkill conditions do not drastically alter the fish community, the black crappie population will be dominated by fish greater than 10 inches. The black crappie appear healthy and near shore sampling with seines and backpack electrofishing in 2010 found age 0 black crappie indicating the population is naturally reproducing.

Other species caught at high abundance in Wilmert Lake were freshwater drum, bigmouth buffalo, and common carp. The freshwater drum catch rates were 121.0 fish/gill net and 12.7 fish/trap net. Both catch rates were greater than expected (8.3 fish/gill net and 3.3 fish/trap net) and were the highest abundances ever documented. The freshwater drum total length ranged from 8 to 15 inches with an average of 10 inches. Nearly 90% of the freshwater drum was less than 11 inches. The bigmouth buffalo catch rates were 6.0 fish/gill net and 3.9 fish/trap net in 2010 which was equivalent to the higher expected range for gill nets and almost 4 times the expected high for trap nets. Bigmouth buffalo ranged from 6 to 27 inches and the mean weight of fish in the trap nets was 7 pounds. The common carp catch rates were 8.0 fish/gill net and 4.1 fish/trap net, which are within the expected range for gill nets (1.0 to 13.8 fish/gill net) and trap nets (1.0 to 5.5 fish/trap net). Common carp ranged in length from 13 to 27 inches with a mean length of 21 inches. Freshwater drum, bigmouth buffalo, and common carp made up 70% of the catch by weight in 2010 and appear to be dominating the Wilmert Lake fish community. Commercial fishing occurs in Wilmert Lake, and in November 2009 approximately 30,000 pounds of freshwater drum, bigmouth buffalo, and common carp were removed.

Some species caught at low abundances in the nets were black bullhead, bluegill, golden shiner, white crappie, and white sucker. All these species had catch rates that were lower than the expected range.

To promote and maintain healthy fish populations, pollution and other inputs need to be controlled. Fish habitats are directly affected by water quality. Nutrient, sediment and other waste inputs can drastically alter the biological, chemical, and physical components of a lake. It is paramount to maintain if not improve the current water quality of Wilmert Lake through watershed management to preserve this fishery for future generations to enjoy.

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