Spearhead

Temperature and dissolved oxygen measurements were collected from the deepest basin in Spearhead Lake on July 30th, 2025. This was done to evaluate the quantity and quality of cold, oxygenated water (i.e., oxythermal habitat) available to Cisco, also known as Tullibee, the most sensitive coldwater species present in this lake. Cisco require a layer of oxythermal habitat that contains water temperatures below 21.2 degrees C (70.2 degrees F) and dissolved oxygen concentrations above 3.0 mg/L. Based on data collected from the deepest basin (maximum sampled depth was 80.0 feet), the water temperature decreased to 21.2 degrees C (70.2 degrees F) at 16.1 feet and the dissolved oxygen concentration decreased to 3.0 mg/L at 25.3 feet at the time of sampling. This layer in the water column was 9.2 feet, indicating oxythermal habitat for Cisco was present. Further, the temperature at which dissolved oxygen decreased to 3.0 mg/L (i.e., TDO3, a single variable to characterize oxythermal habitat) was 12.7 degrees C (54.9 degrees F). TDO3 values cooler than 21.2 degrees C (70.2 degrees F) indicate that oxythermal conditions were suitable for Cisco at the time of the survey. Data collected by the Minnesota Department of Natural Resources during the period of maximum oxythermal stress (July 26th to Aug 24th) in 2022 and 2023 also indicated suitable oxythermal habitat in all years surveyed, with the least favorable conditions recorded in 2022 when the suitable oxythermal habitat layer was 8.4 feet thick. When adequate oxythermal habitat is not available, Cisco are squeezed into unfavorable, warmer water conditions and experience higher levels of stress.

A targeted survey of nearshore fish species in Spearhead Lake was conducted on August 8-9, 2023, by Index of Biological Integrity (IBI) Program staff. Sampling sites were evenly spaced around the lake, and each was sampled by backpack electrofishing and seining with a 50-foot or 15-foot seine, where possible. Backpack electrofishing was completed at nine sampling stations, but one station was sampled from the boat due to site conditions. Similarly, a 50-foot seine was used to sample five stations, a 15-foot seine was used at four stations, and site conditions prevented the use of seines at two stations. Nearshore sampling captured sixteen species of fish including six species that are intolerant of disturbance (i.e., Banded Killifish, Blackchin Shiner, Blacknose Shiner, Iowa Darter, Northern Sunfish, and Rock Bass) and one that is tolerant of disturbance (i.e., Green Sunfish). A concurrent summer trap net survey was also conducted by IBI Program staff. Nine trap nets were set along the shoreline in locations that encompassed multiple habitat types. Trap net sampling captured nine species of fish, including one that is intolerant of disturbance (i.e., Rock Bass). Bluegill comprised a majority of the catch by number, whereas Bowfin comprised a majority by biomass. The nearshore and trap net data were combined with gill net data from a 2022 survey to describe the fish community and provide a fish-based IBI (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. In Minnesota lakes, certain fish species cannot survive without clean water and a healthy habitat (e.g., Blackchin Shiner, Iowa Darter, and Rock Bass), while other species are tolerant of degraded conditions (e.g., Black Bullhead and Green Sunfish). 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. For additional information on the FIBI, search for "lake index of biological integrity" on the mndnr.gov website. Results from this survey indicate that the fish community in Spearhead Lake is healthy as indicated by an FIBI score that exceeds the general use threshold determined for similar lakes. These results are similar to previous survey findings, which indicated that Spearhead Lake is fully supporting for aquatic life use. These results will be considered when the biological health of the lake is assessed during the Mississippi River - Headwaters Watershed assessment process, which will be completed in coordination with MN Pollution Control Agency. A temperature-dissolved oxygen profile was collected in the deepest basin on Spearhead Lake on August 8, 2023, to evaluate the amount of cold, oxygenated water (i.e., oxythermal habitat) available to Cisco, also known as Tullibee. Based on the profile, the top of the thermocline (i.e., the location in the water column with the sharpest transition from warm to cold water) occurred at approximately 16 feet. Dissolved oxygen decreased to below 3.0 mg/L at 35.1 feet, which was below the thermocline, at the time of sampling. The temperature at which dissolved oxygen decreased to below 3.0 mg/L (i.e., TDO3, a single variable to characterize oxythermal habitat) was 6.4°C (43.5°F). TDO3 values cooler than 21.5°C indicate that oxythermal conditions are favorable for Cisco. Dissolved oxygen concentrations below the thermocline indicate that suitable oxythermal habitat for Cisco was available across a range of depths at the time of sampling during the summer of 2023. Data collected in 1985-2010 further indicate suitable oxythermal habitat across years, with the least favorable conditions recorded in 1985. When inadequate oxythermal habitat is available, Cisco are squeezed into unfavorable, warmer water conditions and therefore experience higher levels of stress.

Spearhead Lake (29-0239-00) is a 188.89-acre lake with a maximum depth of 81 feet located near Becida, MN. Park Rapids Fisheries staff conducted a survey targeting near shore fish species on August 1, 2022, to assess populations of non-game and small sport fish. Ten 100-foot sampling sites were evenly spaced around the lake shore, sampling a variety of habitat types. Each site was sampled by backpack electrofishing and seining with a 50-foot or 15-foot 1/8th-inch mesh seine, depending on habitat conditions. During this assessment, four sites were sampled with a 15-foot seine. Site conditions prevented the use of seines at six sites. Backpack electrofishing was done at all 10 sites with five being conducted from the side of the boat. Nearshore sampling captured ten species of fish including zero species intolerant of disturbance. Other species sampled during the nearshore effort included Black Bullhead, Bluegill, Central Mudminnow, Green Sunfish, hybrid sunfish, Iowa Darter, Largemouth Bass, Northern Sunfish, Rock Bass, Yellow Bullhead, and Yellow Perch. Nearshore catches will be used along with gill net and trap net catch data from a standard fisheries survey conducted on May 31, 2022 to calculate a fish-based Index of Biotic Integrity (IBI) score, which is indicative of the health of Spearhead Lake. This survey is contributing to a watershed assessment process in coordination with MN Pollution Control Agency. Spearhead Lake is located in the Mississippi River - Headwaters Watershed.

Based on Minnesota DNR survey data, anglers target Rock Bass, Walleye, Yellow Perch, Black Crappie, and Bluegill in Spearhead. See the full species list above for catch rates, size structure, and quality scores.

We don't have a confirmed public access point on record for Spearhead. Check the DNR LakeFinder page for current access details before you go.

Spearhead has a maximum depth of 81 feet, per Minnesota DNR data.

The most recent Minnesota DNR survey data for the main sport fish in Spearhead is from 2023.

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