In many regions, long-term drought is altering patterns of water use and reservoir storage, which in turn can facilitate the spread of non-native fishes. Decreasing supply and increasing demand in USA’s Colorado River basin has reduced water storage in the country’s two largest reservoirs. In 2022, historically low water levels in Lake Powell and associated fish entrainment and warming of release temperatures led to the first observations of non-native smallmouth bass (Micropterus dolomieu) reproduction in the Grand Canyon segment of the Colorado River downstream from Lake Powell and Glen Canyon Dam. In the Colorado River basin, smallmouth bass are considered a primary threat to the recovery of federally listed, endemic species, such as the humpback chub (Gila cypha). To assist managers confronting this range expansion, USGS developed models to 1) forecast the potential for smallmouth bass establishment and 2) design Glen Canyon Dam operational alternatives to slow or stop this invasion. Based on this modeling effort, the Bureau of Reclamation began a management experiment in 2024, referred to as a ‘cool mix’ treatment, in which a portion of the dam’s daily discharge was released through the deeper outlet works, which pull colder water from the reservoir. Cool mix water temperature targets were chosen with goals of minimizing or eliminating spawning and minimizing somatic growth. Since the implementation of this designer flow, to date there has been no evidence of smallmouth bass reproduction in this stretch of the Colorado River. This USGS modelling effort highlights the lesser-known impacts of drought on ecological invasions and provides an example of rapid ecological forecasting to inform time-sensitive management.