Abstract Sound observations are essential for understanding lake–atmosphere energy exchanges, which govern lake water levels and energy budgets and are critical for weather forecasting, water quality assessment, and navigation. While advances have been made with observation programs on large lakes, such as North America’s Laurentian Great Lakes, current fixed-location platforms measure relatively little of the spatial variability in turbulent fluxes across these large systems. Here, we apply ship-borne eddy-covariance-derived turbulent flux measurements that reveal the presence of evaporation zones, defined as contiguous areas of upward latent heat fluxes, separated from areas of downward latent heat fluxes by turbulent flux boundaries. Boundaries continue to migrate with time, with atmospheric conditions and surface water temperatures, but collapse as the lake warms through summer and the entire lake area begins to evaporate. These results have implications for how evaporation should be estimated, which would be improved with distributed approaches. Coupled lake–atmosphere representation in predictive platforms is likely necessary to capture these spatial dynamics, which would improve water level prediction, lake thermal and ecosystem characterization, and weather forecasting. Last, the date of turbulent flux boundary collapse could be used as a new metric of lake function and state that augments existing metrics such as date of stratification.
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