Analysis of spatially-explicit ecological phenomena in aquatic ecosystems is impeded by a lack of knowledge of, and tools to delimit, spatial patterns of material supply to point locations. Here we apply the concept of “resource sheds” to coasts and watersheds. Resource sheds are defined as source areas from which materials are derived for an individual, population, or location, over a specified time interval. Resource shed total spatial extent, and relative contributory importance, for selected point locations in Lake Erie were delimited, including extension into the Maumee River watershed. Resource shed size and orientation varied with in-lake circulation patterns, terrestrial precipitation patterns, time interval, and season. In-lake resource sheds for sites near river mouths and along shorelines showed less variation in size and shape with time and between seasons compared with sites further off shore. Source areas within watersheds supplying water to off-shore locations were estimated by linking the output of hydrologic and hydrodynamic models. Potential applications of the resource shed concept include the study and management of aquatic ecosystems and use as an environmental forensics technique. Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy.