Eastern hemlock (Tsuga canadensis) is a long-lived, shade tolerant tree that is considered a foundation species, especially in riparian corridors. Hemlock stands are characterized by a dense evergreen canopy that creates a unique microenvironment within a broader deciduous forest landscape in eastern North America. Hemlock serves a distinct ecohydrological roles: it maintains year-round transpiration rates, and it increases canopy interception rates. Since the 1950s, the non-native hemlock woolly adelgid (I), or HWA, has caused widespread mortality resulting in permanent reductions in winter transpiration rates. In the southern Appalachians, hemlock loss saw permanent reductions in watershed yield and increases in peak flow. Forest Service scientists used MODIS imagery and tree data from Forest Inventory and Analysis plots located within sub-watersheds of the Chesapeake Bay to estimate hemlock basal area. Watersheds where hemlock basal area is at least 6 percent are located in northern Pennsylvania and southern New York. In partnership with the Pine Creek Watershed Council (Tioga County, Pennsylvania) and the U.S. Geological Survey, Forest Service scientists are prioritizing conservation efforts for field monitoring of hydrologic processes and supplemental conifer planting to protect the unique cold water heritage and trout streams in anticipation of hemlock decline.