The performance of 76 kHz positional acoustic telemetry is challenged by acoustic conditions in the tailrace of a hydroelectric dam.

Background: Positional acoustic telemetry permits high-resolution (2D and 3D) tracking of tagged fish based on the speed of sound and time at which acoustic signals are detected at independent receivers. Such positional data has important implications for understanding fish behavior in hydropower tailraces, where movement and fishway passage may be influenced by complex hydraulic conditions. However, environmental features common to these settings-such as rocks, vegetation, bubbles, and suspended particles-can reflect, scatter, or absorb acoustic signals, contributing to spatial and temporal variation in positioning error. Therefore, validating system performance in tailrace environments is important for study design and interpretation. We evaluated the performance of a 76 kHz positional acoustic telemetry system (LOTEK MAP) in the tailrace (0-500 m downstream) of a large (672 MW generating capacity) hydroelectric dam, an environment characterized by reflective surfaces, complex hydraulics, and ambient noise from power generation. Methods: We quantified positional accuracy ( Results: The array nearest the power station ( Conclusions: Performance of the telemetry system was limited by environmental conditions that influenced signal propagation at complex spatial and temporal scales and would ultimately challenge the interpretation of positional data for free-swimming fish in the tailrace. The telemetry system is likely not suitable for studies that require frequent and reliable positions in hydropower dam tailrace environments. Supplementary Information: The online version contains supplementary material available at 10.1186/s40317-025-00420-6.