PiSCES predicts a fish assemblage for any stream in the conterminous United States by referencing HUC-based distributional information for over 1,000 native and non-native species obtained from NatureServe, the USGS and the Peterson Field Guide to Freshwater Fishes of North America (Page and Burr 2011). In addition to using current geographic distributions, PiSCES can refine potential communities to reflect information on species rarity, stream size preferences and occurrence envelopes for water quality metrics (pH, conductivity, turbidity, dissolved oxygen) and stream characteristics (watershed area, mean width, depth, and slope). PiSCES can also create an abundance distribution for a fish community using the known inverse relationship between the abundance of a species and its maximum body size.