National Water-Quality Assessment (NAWQA) Program
Overview maps (gif) of study unit boundaries: cycle 1 || cycle 2
Boundaries and codes for the areas studied during the first decade of the NAWQA program from 1991-2001 - nawqacyc1
Boundaries and codes for the areas to be studied during the second decade of the NAWQA program from 2001-2012 - nawqacyc2
Generalized boundaries and codes for the areas studied during the first decade of the NAWQA program from 1991-2001 - nawqagencyc1
Generalized boundaries and codes for the areas to be studied during the second decade of the NAWQA program from 2001-2012 - nawqagencyc2