This line shapefile of evolutionary significant unit boundaries was compiled from various sources based on written descriptions in National Marine Fisheries Service (NMFS) status reviews (available upon request) and mapping provided by NMFS. An Evolutionary significant unit, or ESU, of Pacific salmon is considered to be a "distinct population segment" and thus a "species" under the Endangered Species Act. Initial boundaries were derived from USGS 1:250,000 scale hydrologic unit boundaries. Drainage basin delineation from blockages was based on 1:100,000 stream hydrography and/or and available digital topography(1:250,000). Species do not necessarily inhabit all drainages or river reaches depicted.This dataset includes evolutionary significant unit (ESU) polygons depicting major basins within the current known range of each ESU, and were modified based on migration blockages and known fish distribution.