Attributes for NHDPlus Catchments (Version 1.1): Level 3 Nutrient Ecoregions, 2002
This data set represents the area of each level 3 nutrient ecoregion in square meters,  compiled for 
every catchment of NHDPlus for the conterminous United States. The source data are from the 2002 
version of the U.S. Environmental Protection Agency's (USEPA) Aggregations of Level III Ecoregions 
for National …