The Nature Conservancy developed a subwatershed prioritization to help identify areas of high diadromous fish conservation potential along the Atlantic Coast. A suite metrics were calculated in a GIS for each USGS HUC12 to measure population and habitat factors which are relevant to river herring and shad. A subset of these metrics were then selected and assigned relative weights to develop prioritizations for alewife, blueback herring, and American shad. The high priority subwatersheds in these results are areas where conservation activities to support diadromous fish could have the greatest impact, however they are agnostic of any specific action. In some subwatersheds, a fish passage project may be the most appropriate conservation action while in another it may be a marsh restoration. Thus, the results are intended to be used as a regional-scale screening-level tool, in concert with local-scale information and expertise; they are not a prescription for action.