The chemical, physical and biological characteristics of surface waters are interrelated phenomena. Making greater use of the stream biota to determine existing, and to forecast future, water quality in the stream offers promising possibilities. Plankton studies within the National Water Quality Network have included extensive work designed to permit application of the principle of diatom species diversity to the development of water quality indices. The studies required development of new laboratory analytical techniques, as well as preliminary application of the methodology to surface water samples from the many diverse Network sampling points. Published herein are data from samples collected in the 2-year period July 1959 through June 1961 at 65 of the Network stations.