South Turtle

A targeted survey of the nearshore fish community in South Turtle Lake was conducted by Fisheries Index of Biological Integrity (IBI) Program Staff starting July 24, 2018 on South Turtle Lake. Fourteen sampling sites were evenly spaced around the lake and each was sampled by backpack electrofishing and seining with a 15-foot or 50-foot seine, where possible. Backpack electrofishing was completed at all 14 sites with five sites sampled from the boat. Similarly, a 50-foot seine was used to sample six sites, a 15-foot seine was used at three sites, and soft sediments with abundant vegetation and deep water prevented the use of seines at five sampling site. Nearshore sampling captured 17 native species of fish including five species that are intolerant of disturbance (Banded Killifish, Blackchin Shiner, Blacknose Shiner, Iowa Darter, and Pugnose Shiner) and 1 species that is tolerant of disturbance (Green Sunfish). Data from this targeted nearshore survey is combined with trap net and gill net data from an August 2017 standard survey to describe the fish community and provide a Fish-based Index of Biological Integrity (FIBI) score. The FIBI uses fish community data to measure a lake's health, and the types of fish species present can help identify any stressors that may be negatively affecting the lake environment. The FIBI score, composed of several fish community diversity and composition metrics, indicates the overall health of a lake by comparing it to what is expected for a healthy lake. The FIBI score for South Turtle Lake from this survey is just below an impairment threshold for aquatic life use determined for similar lakes. For additional information on the FIBI, search for "lake index of biological integrity" on the mndnr.gov website. Data from this survey will contribute biological information about the health of the fish community to the Pomme de Terre River Watershed assessment of surface waters process completed in coordination with MN Pollution Control Agency.

South Turtle Lake is a 630-acre mesotrophic (moderately fertile) lake located in central Otter Tail County approximately four miles east of Underwood, MN. South Turtle Lake is located within the Pomme De Terre River Watershed. The immediate watershed is composed primarily of agricultural land interspersed with hardwood woodlots. The maximum depth is 35 feet; however, 63% of the lake is less than 15 feet in depth. The secchi disk reading was 17.5 feet. Previous secchi disk readings ranged from 5.5 to 15.8 feet. The north and west shorelines have been extensively developed. Homes, cottages, and resorts compose the majority of the development. A state owned concrete public access is located off of County Road 122 along the north shoreline of the lake. Shoal water substrates consist primarily of sand, gravel, and rubble. South Turtle Lake is composed of two distinct basins. The west basin is deeper and more developed. A large stand of hardstem bulrush is located along the southeast shoreline of this basin. The east basin is shallower (less than 15 feet) and less developed. Hardstem bulrush and cattails are prevalent along the shoreline of this basin. Emergent plants provide valuable fish and wildlife habitat, and are critical for maintaining good water quality. They provide critical spawning and nursery habitat for fish species such as Northern Pike, Largemouth Bass, and sunfish. They protect shorelines from erosion and can actually absorb and break down pollutants. Because of their ecological importance, bulrush and cattails may not be removed without a DNR permit. South Turtle Lake can be ecologically classified as a bass-panfish type of lake and this is reflected in the assemblage of the fish community. The dominant gamefish species are Northern Pike, Largemouth Bass, Bluegill, and Black Crappie. The prolificacy of these species can be attributed to the abundance of suitable spawning habitat that is available. A moderate-density Northern Pike population exists. Northern Pike ranged in length from 13.0 to 30.9 inches with an average length and weight of 20.4 inches and 2.0 pounds. Pike attain an average length of 22.9 inches at four years of age. Age and length data indicate that a balanced Largemouth Bass population exists. Age data indicate that bass reproduction is consistently good. Bass ranged in length from 7.3 to 18.7 inches with an average length and weight of 13.0 inches and 1.3 pounds. Bass attain an average length of 13.3 inches at five years of age. Black Crappies have remained consistently abundant over the recent series of surveys. Black crappies ranged in length from 7.9 to 13.1 inches. Thirty percent of the crappies were 10.0 inches or greater in length. Black crappies attain an average length of 9.5 inches at six years of age. Bluegills have also remained abundant. Bluegill reproduction has been consistently good. Twenty-eight percent of the Bluegills were 7.0 inches or greater in length. Bluegills attain an average length of 6.7 inches at five years of age. Walleye abundance is low. Walleyes ranged in length from 16.6 to 24.8 inches with an average length and weight of 20.6 inches and 3.4 pounds. Anglers can help maintain the quality of angling by practicing selective harvest. Selective harvest encourages the release of medium to large size fish while allowing the harvest of the more abundant smaller fish for table fare. Releasing the medium to large fish will ensure that the lake will have enough spawning age fish on an annual basis and will provide anglers with more opportunities to catch large fish in the future. South Turtle Lake is not listed as an infested water. Aquatic invasive species are threatening Minnesota waters. The non-native species can potentially harm water quality, water recreation, aquatic habitat, native species, and fish populations. Anglers can help prevent the introduction and spread of invasive species by following watercraft transportation laws. Anglers are required to remove all visible plants, mud, and other prohibited invasive species and drain all water from their boat prior to leaving the water access.

Near shore fish sampling information was gathered to evaluate the fish index of biotic integrity (IBI) for South Turtle Lake. IBI data was collected in conjunction with Minnesota Pollution Control Agency watershed sampling. Fourteen 100-foot sampling sites were evenly spaced around the lake shore, sampling a variety of habitat types. Each site is sampled by backpack electrofishing and seining with a 50-foot or 15-foot 1/8th-inch mesh seine, depending on habitat conditions. Sites where habitat conditions did not allow for seining were backpack electrofished unless conditions proved difficult for walking. These sites were backpack shocked from the boat. Fourteen fish species were represented, including young of the year gamefish species such as Northern Pike, and Largemouth Bass. Non-game species sampled included Banded Killifish, Iowa Darter, and Pugnose Shiner.

Based on Minnesota DNR survey data, anglers target Largemouth Bass, Walleye, Northern Pike, Black Crappie, and Hybrid Sunfish in South Turtle. See the full species list above for catch rates, size structure, and quality scores.

Minnesota DNR records list public access for South Turtle. Check the DNR LakeFinder page for the launch type and directions before you go.

South Turtle has a maximum depth of 35 feet, per Minnesota DNR data.

The most recent Minnesota DNR survey data for the main sport fish in South Turtle is from 2017. Surveys this old should be treated with some caution — fish populations change over time.

No invasive species are on record for South Turtle in Minnesota DNR data. Always clean, drain, and dry your equipment to help keep it that way.