This project will estimate the numbers of Snake River fine-spotted cutthroat trout and other native fish that are drawn into (or entrained in) the Granite Supplemental Ditch in the southwest area of Grand Teton National Park (GTNP). Fish entrainment has been identified as a potentially significant source of fish loss in Wyoming and throughout the western United States. Recent efforts at the Spread Creek and Granite Supplemental irrigation systems have identified entrainment as a conservation issue for native fish that could be mitigated. Fish entrainment at both these locations is caused by the movement of fish from streams and rivers into irrigation canals or ditches, where most fish become isolated from the Snake River and its tributaries. Cooperative efforts of Wyoming Game and Fish Department (WGFD), Trout Unlimited (TU), and GTNP in 2017 and 2018 determined that approximately 75–93% of cutthroats that become entrained died in the canal system due to predation or acute habitat loss. Thus, understanding how many fish enter this specific ditch system is paramount to understanding the potential population-level effects of entrainment. Assessing and mitigating fish entrainment is critical to regional populations of trout. In smaller ditch systems, such as Spread Creek, entrained fish have been salvaged and returned to main streams through interagency efforts. However, the size of the Granite Supplemental system and poor access due to property ownership patterns would not make salvaging and transporting fish from the system feasible or effective.