Attributes for NHDPlus Catchments (Version 1.1) for the Conterminous United States: Level 3 Ecoregions
This data set represents the estimated area of level 3 ecological landscape regions (ecoregions), 
as defined by Omernik (1987), compiled for every catchment of NHDPlus for the conterminous 
United States. The source data set is Level III Ecoregions of the Continental United States 
(U.S. Environmental Protection …