Heron Lake (South Heron)

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The Heron Lake system includes 8,151 acres of discontinuous lake basin. Seventy-eight percent of this acreage is included in North Heron (3,526 acres) and South Heron (2,845 acres). The watershed comprises 472 square miles (302,080 acres) for a watershed-to-lake ratio of 37 to 1. Heron Lake has a renowned history for waterfowl hunting because of the historical production of aquatic vegetation. In 1973, it was designated by the Commissioner of the Natural Resources as a wildlife management lake following public hearings in the local area. The wildlife management goal is to improve the lake system for waterfowl, fur bearers, and numerous other species of game and nongame wildlife traditionally found in Southern Minnesota. Effective management requires periodic but temporary draw-downs, such as occur during times of drought. Extended periods of high water destroy the aquatic vegetation needed by wildlife. Fish species can also destroy aquatic vegetation. Common carp invaded South Heron Lake around 1918 and have made it difficult to maintain production of aquatic vegetation for northern pike spawning and for waterfowl foraging. Efforts to reclaim South Heron with rotenone were conducted during the winter of 1997-98 with little success due to an unexpected thaw causing dilution of rotenone. Fisheries management contributes to the overall goal of wildlife management by managing the lake to include a fishable northern pike population with fish 30 inches or greater found in the sample. Additionally, yellow perch and walleye are maintained by stocking. Addition of northern pike, yellow perch and walleye is beneficial to the lake because they may act as predators to keep common carp and other undesirable fish species in low abundance. A population assessment was conducted on South Heron Lake during the week of June 13, 2011 using 1 gill net and 13 trap nets to assess the current management goals.



Northern pike have been stocked in South Heron Lake to augment the population and achieve the management goals with adult (1998 and 1999), fingerling (2006), and fry (1998 and 2009) northern pike. The northern pike gill net catch rate in 2011 was 27.0 fish per gill net which was greater than the normal range of 1.2 to 7.8 fish per gill net and the greatest observed catch rate since 1987. Additionally, the 2011 gill net catch rate was greater than the long-term average of 14.3 fish per gill net. South Heron Lake has historically been sampled with trap nets (11 years of data since 1981) while gill nets are used infrequently (5 years of data since 1987). The 2011 trap net catch rate was 1.2 fish per trap net which is one of the lowest catch rates in Heron Lake and less than the long-term average catch rate of 5.6 northern pike per trap net. The high gill net catch rate in combination with the low trap net catch rate indicates the sporadic nature of northern pike and the need for gill nets and trap nets to effectively sample the northern pike population in Heron Lake. The average length of northern pike in the gill net catch was 16.9 inches and the average length in the trap net catch was 21.5 inches with the largest fish being 32 inches. The size structure of the northern pike population was less than desired. The population is currently dominated by smaller fish in the 14 to 21 inch range. The condition of the northern pike in the sample was average indicating a population that is of expected weight for their length indicating adequate foraging success. Overall, the northern pike population appears to be maintaining itself near the management goal with good abundance and good body condition. Fishing for northern pike in South Heron Lake can be good with larger fish caught at opener in cooler water and again in the fall.



The yellow perch catch rates in 2011 were 13.0 fish per gill net and 0.6 fish per trap net. The catch rates were within the normal ranges for gill nets (3.0 to 22.5 per net) and trap nets (0.3 to 2.6 per net) meeting the management goal, but they were less than the long-term catch rates of 37.4 per net and 7.9 per net for gill nets and trap nets respectively. The average length of yellow perch in the sample was 7.2 inches in the gill net and 8.3 inches in the trap nets with fish ranging from 5.7 to 11.4 inches in the samples. The size structure indicated a population that is dominated by fish in the 5 to 8 inch range. The overall condition of the yellow perch in the sample was below average which is most likely a result of a decreased body condition shortly after the spring spawning period and not entirely related to poor foraging success. Overall, the yellow perch population is within the normal range for South Heron Lake but the length and condition of the population does not indicate a population that would satisfy yellow perch anglers at this point. At this stage in their population development, yellow perch appear to be a forage base for other species. Given several years of population maturity, the yellow perch angling opportunity on South Heron Lake will improve and the population will contain fish of a larger average size.



Walleye are maintained with stocking in South Heron Lake and for the last 2 years (2010 and 2011) walleye fry in excess of 1 million each year have been stocked. Although it would not be considered a high priority for walleye fry given the shallowness of Heron Lake, the hatchery has had good hatching success so surplus walleye fry are stocked as an additional predator. The gill net catch rate in 2011 was 27.0 fish per gill net which is greater than both the normal range of 3.2 to 15.3 per net and the long-term average of 6.5 per net. The 2011 catch rate is also the greatest on record since 1987. The trap net catch rate was 0.1 fish per trap net, less than the normal range of 0.3 to 1.7 fish per net and long-term average of 0.2 per net, but trap net catch rates are poor indicators of walleye abundance and gill nets are more reliable. It appears the 2010 fry stocking is contributing to the population as 54% of the sample was from that age class. The other ages represented in the sample were age 2 (42% of sample), and age 3 (4% of sample), both which were not stocked year classes and most likely a result of emigrants from other connected lakes or rivers or from natural reproduction. As you might expect, there are several walleye managed lakes above Heron Lake. The average length of walleye in the gill net sample was 12.5 inches with a range from 9.6 to 18.7 inches. The lengths of walleye in the sample indicated a population that is nearing a balanced size structure with a good range of sizes present. The overall condition of the population was good for a late spring sample and indicates a population that is foraging successfully. Overall, the establishment of walleye as a predator to control unwanted species in South Heron Lake is successful and stocking will continue to maintain the population. As a byproduct, a fantastic angling opportunity for walleye exists in South Heron. South Heron Lake is vast and shallow, but walleye anglers that commit time to find the walleye will also find good success. Walleye angling could be successful for those anglers that can figure out the patterns of walleye in South Heron.



Other species sampled in the gill net and trap nets were bigmouth buffalo, black bullhead, black crappie, common carp, creek chub, tadpole madtom, white crappie, white sucker, and yellow bullhead for a total of 12 species including northern pike, yellow perch, and walleye. Bigmouth buffalo, black bullhead, black crappie, white crappie, and white sucker were below long-term catch averages but within normal ranges for most species. However, common carp catch rates were greater than the long-term catch average and greater than the normal range indicating the need for continued predator stocking in future years. Creek chub, tadpole madtom, and yellow bullhead are infrequently sampled but near average catch rates for South Heron Lake.


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 alter the biological, chemical, and physical components of a lake. It is paramount to maintain if not improve the current water quality of South Heron Lake through watershed best management practices to preserve this fishery for future generations to enjoy.



Prepared by Nate Hodgins

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