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Abstract. Four adjacent lakes (Arco, Budd, Deming, and Josephine) within Itasca State Park in Minnesota, USA, are reported to be meromictic in the scientific literature. However, seasonally persistent chemoclines have never been documented. We collected seasonal profiles of temperature and specific conductance and placed temperature sensor chains in two lakes for ∼1 year to explore whether these lakes remain stratified through seasonal mixing events and what factors contribute to their stability. The results indicate that all lakes are predominantly thermally stratified and are prone to mixing in isothermal periods during spring and fall. Despite brief, semi-annual erosion of thermal stratification, Deming Lake showed no signs of complete mixing from 2006–2009 and 2019–2022 and is likely meromictic. However, the other lakes are not convincingly meromictic. Geochemical data indicate that water in Budd Lake, which contains the most water, is predominantly sourced from precipitation. The water in the other three lakes is of the calcium–magnesium–bicarbonate type, reflecting a source of water that has interacted with the deglaciated landscape. δ18OH2O and δ2HH2O measurements indicate the lakes are supplied by precipitation modified by evaporation. Josephine, Arco, and Deming lakes sit in a valley with likely permeable sediments and may be hydrologically connected through wetlands and recharged with shallow groundwater, as no streams are present. The water residence time in meromictic Deming Lake is short (100 d), yet it maintains a large reservoir of dissolved iron, indicating that shallow groundwater may be an additional source of water and dissolved ions. All four lakes develop subsurface chlorophyll maxima layers during the summer. All lakes also develop subsurface oxygen maxima that may result from oxygen trapping in the spring by rapidly developed summer thermoclines. Documenting the mixing status and general chemistry of these lakes enhances their utility and accessibility for future biogeochemical studies, which is important as lake stratification and anoxia are becoming more prevalent due to changes in climate and land use. 

Depth profiles of water column chemical and physical properties were assessed with seasonal-scale frequency from Little Comfort from September 2023 to June 2024 and from Keewahtin Lake in September 2023. The data were collected to assess mixing status, major geochemical constituents within the lake, and mineral precipitation reactions. Several parameters were routinely measured with deployable probes at meter or sub-meter resolution at the deepest location in each lake. Water samples were also collected for laboratory analysis.