Non-native crayfish threaten native aquatic and semi-aquatic species via modification of aquatic habitats and food webs, and via depredation and competition. In Arizona and New Mexico, management of crayfish is challenged by a paucity of knowledge about factors governing their distribution and population dynamics in space and time. Virile (Faxonius virilis) and red swamp crayfish (Procambarus clarkii) have been documented in at least 22 of 84 HUC8 watersheds within the Lower Colorado River Basin, largely through opportunistic surveying efforts. However, systematic population surveys conducted across key environmental gradients are needed (1) to identify the environmental conditions that predict occupancy, local extinction, and colonization across sites; and (2) to understand how environmental context shapes potential negative interactions with native species. This project will use existing biological collections and GIS-based environmental data to design and implement a 3-year survey of crayfish at 108 sites in the Gila and Little Colorado River basins, both within the Lower Colorado River basin. Sites will span gradients of physiography, land use, and flow intermittency within each of 11 HUC8 watersheds that collectively harbor 31 Species of Greatest Conservation Need (SGCNs) representing native invertebrates, fishes, amphibians, and reptiles. In situ electrical resistance loggers also will be deployed continuously throughout the project to quantify flow intermittency. Crayfish surveys will be used to parameterize dynamic occupancy models to identify environmental drivers of detection, occupancy, colonization, and extinction. Next, ensemble-based species distribution models will be implemented to map presence-absence of crayfish for 61,450 interconfluence stream reaches in the Gila and Little Colorado River basins. These high-resolution maps will be integrated with existing maps of 31 SGCNs (HabiMap™ Arizona) to quantify the potential co-occurrence and interactions between crayfish and SGCNs. Products from this project will inform conservation actions by facilitating spatial prioritization of crayfish eradication efforts and native species recovery.