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Stable water isotopes of oxygen and hydrogen are a tool for studying atmospheric processes and watershed hydrology, and dynamics of groundwater and stream water can be studied using isotopic composition. We use the Green Lakes Valley watershed in Colorado, which contains a small glacier and other features typical of alpine headwaters in western North America, to assess the elevational controls on isotopic composition. Cryospheric features within the watershed include the Arikaree Glacier, a small rock glacier, and snowfields. The basin is the source of North Boulder Creek, and there are six lakes connected by North Boulder Creek that drain to the South Platte River, an important water source in Colorado. Across the 700 ha watershed, the elevation ranges from 3250 to about 4000 m, and there is an over 500 m difference between the highest and lowest elevation surface water sampling sites. Similar to precipitation, surface water isotopic composition is controlled by elevation. It is essential to better establish how elevation controls isotopic composition in the surface water and groundwater and determine lapse rates for oxygen-18 and deuterium. This work forms the basis for potential future studies on hydrologic and hydrogeologic processes in snow-covered alpine catchments.