Increasing concentrations of dissolved organic carbon (DOC) in the northeastern U.S. have been attributed to two potential mechanisms: recovery from acidification and changing climate. Maine's high‐elevation lakes (>600m) could potentially provide unique insight into the response of surface water chemistry to declining acidic deposition and interannual climate variability. The geochemical response in 29 lakes was analyzed during 30 years of change in sulfate ( SO42−) deposition and climate. All 29 lakes exhibited positive trends in DOC from 1986 to 2015, and 19 of 29 lakes had statistically significant increases in DOC throughout the study period. These results illustrate a region‐wide change from low‐DOC lakes (<5mg/L) to moderate DOC lakes (5–30mg/L). Increasing DOC trends for these high‐elevation lakes were more consistent than for lower elevation lakes in the northeastern U.S. A linear mixed effects model demonstrated that lake water SO42− and climate variables describe most of the variability in DOC concentrations (r2 = 0.78), and the strongest predictor of DOC concentration was an inverse relationship with SO42−. Due to SO42− concentrations trending toward preacidification levels and projections of a warmer, wetter, and more variable climate, there is uncertainty for the future trajectory of DOC trends in surface waters. Long‐term monitoring of Maine's high‐elevation lakes is critical to understand the recovery and response in surface water chemistry to a changing chemical and physical environment in the decades ahead.

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