Thumb

Temperature and dissolved oxygen (DO) measurements were collected from the deepest basin in Thumb Lake on July 30th, 2025, 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. During the summer, 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 the profile from the deepest basin (maximum sampled depth 55.8 feet), the water temperature decreased below 21.2 degrees C (70.2 degrees F) at 8.8 feet and the dissolved oxygen concentration decreased to 3.0 mg/L at 49.6 feet at the time of sampling. The thickness of this layer of water in the water column was 40.8 feet, indicating that oxythermal habitat was present for Cisco. Further, the temperature at which dissolved oxygen decreased to 3.0 mg/L (i.e., TDO3, a single variable to characterize oxythermal habitat) was 4.2 degrees C (39.6 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 late summer period of maximum oxythermal stress (July 26th to Aug 24th) in 2024 also indicates suitable oxythermal habitat. When inadequate oxythermal habitat is available, Cisco are squeezed into unfavorable, warmer water conditions and experience higher levels of stress.

Temperature and dissolved oxygen (DO) measurements were collected from the deepest basin in Thumb Lake on July 30th, 2025, 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. During the summer, 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 the profile from the deepest basin (maximum sampled depth 55.8 feet), the water temperature decreased below 21.2 degrees C (70.2 degrees F) at 8.8 feet and the dissolved oxygen concentration decreased to 3.0 mg/L at 49.6 feet at the time of sampling. The thickness of this layer of water in the water column was 40.8 feet, indicating that oxythermal habitat was present for Cisco. Further, the temperature at which dissolved oxygen decreased to 3.0 mg/L (i.e., TDO3, a single variable to characterize oxythermal habitat) was 4.2 degrees C (39.6 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 late summer period of maximum oxythermal stress (July 26th to Aug 24th) in 2024 also indicates suitable oxythermal habitat. When inadequate oxythermal habitat is available, Cisco are squeezed into unfavorable, warmer water conditions and experience higher levels of stress.

Temperature and dissolved oxygen (DO) measurements were collected from the deepest basin in Thumb Lake on July 30th, 2025, 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. During the summer, 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 the profile from the deepest basin (maximum sampled depth 55.8 feet), the water temperature decreased below 21.2 degrees C (70.2 degrees F) at 8.8 feet and the dissolved oxygen concentration decreased to 3.0 mg/L at 49.6 feet at the time of sampling. The thickness of this layer of water in the water column was 40.8 feet, indicating that oxythermal habitat was present for Cisco. Further, the temperature at which dissolved oxygen decreased to 3.0 mg/L (i.e., TDO3, a single variable to characterize oxythermal habitat) was 4.2 degrees C (39.6 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 late summer period of maximum oxythermal stress (July 26th to Aug 24th) in 2024 also indicates suitable oxythermal habitat. When inadequate oxythermal habitat is available, Cisco are squeezed into unfavorable, warmer water conditions and experience higher levels of stress.

Based on Minnesota DNR survey data, anglers target Walleye and Northern Pike in Thumb. 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 Thumb. Check the DNR LakeFinder page for current access details before you go.

The most recent Minnesota DNR survey data for the main sport fish in Thumb is from 1980. Surveys this old should be treated with some caution — fish populations change over time.

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