Cold-water trout habitat in Wisconsin is projected to substantially decrease as a result of climate change. The extent of habitat loss depends, in part, on groundwater discharge to streams, which can provide cool-water refuges for trout. Survey hydrogeologists used field measurements and models of groundwater flow and stream temperature to evaluate how climatic changes are likely to affect groundwater discharge and stream temperatures in the Marengo River headwaters in northern Wisconsin. This improved understanding of system dynamics may help management of the watershed for trout survival. Report, groundwater flow model, geodatabase, and data available for download.