Background: The Nonindigenous Aquatic Species (NAS) Database functions as a repository and clearinghouse for the occurrence of nonindigenous aquatic species information from across the United States. The Database contains locality information on more than 1,300 species introduced as early as 1800, including freshwater vertebrates and invertebrates, aquatic plants, and marine fishes. Taxa include both foreign species and North American native species that have been translocated outside of their natural range. Locality data are derived from many sources, including scientific literature; Federal, State, and local natural resource monitoring programs; museum collections; news agencies; and direct submission through online reporting forms. To effectively identify and record new introductions for North American native taxa, a robust estimate of their natural native ranges is required. Previously, the NAS Database has used native range information for fishes provided by NatureServe, which was collected from State natural heritage program inventory data and published State fish books. Although these range maps represent an essential first step in assembling native range data, the NatureServe data has varied for many species due to initial data assumptions (i.e., species presence = nativity). Additionally, NatureServe native ranges exhibit watershed gaps for many species. NAS program staff members have made thousands of corrections to these data internally and periodically communicate these changes back to NatureServe. Methods: Native ranges were developed from several data sources. Dr. Dana Infante, Michigan State University, provided the NAS program with occurrence (presence) data from 40-50 Federal, State, museum, and university data providers gathered during her work on the National Fish Habitat Partnership (NFHP). Although many data providers have offered datasets with no restrictions, some have restrictions on redistribution. In addition to the NFHP data, we utilized occurrence datasets for United States museum collections from Biodiversity Information Serving Our Nation (BISON), National Science Foundation's VertNet, FishNet 2 (fish collections in natural history museums, universities, and other institutions), Multistate Aquatic Resources Information System (MARIS) data and Global Biodiversity Information Facility (GBIF), along with a review of State fish books and other primary literature, to complete native range data maintained locally in the NAS Database. Occurrence datasets will be combined into larger, species-specific datasets for further processing at a hydrologic unit code (HUC). We will use GIS analyses to identify watershed occurrence at the eight-digit (HUC8) and twelve-digit (HUC12) level, using the 2015 version of the Watershed Boundary Dataset. HUCs containing known nonindigenous occurrences will be removed from the native range. Watershed gaps (i.e., a HUC that lies between two that are identified as part of the native range) will be investigated using historical literature to identify data gaps from actual range gaps. We will supply native range data by HUC8 (and HUC12 where possible) for 320 species listed below. These data will be provided as a comma-separated values (CSV) file and be made available on the NAS website via web services application programming interface (API).