Environmental effects assessment at Canada’s tidal energy test site in the Bay of Fundy includes quantifying fish encounters with marine hydrokinetic (MHK) devices. Acoustic tags have been implanted within the body cavities of fish so their presence could be detected but converting detections to encounters requires also knowing the probability that a transmission from an acoustic tag will be detected. Here we report probabilities of detection obtained from multiple detection range test experiments. Measurements from moored acoustic receivers show probability of detection can be diminished by more than an order of magnitude as current speed increases. Separate hydrophone measurements showed ambient sound levels also increased (~ 10 − 20 dB near the tag frequency) with current speed but this does not entirely account for the reduced detection efficiency. Detection range test experiments using drifters to suspend receivers and tags at mid water column resulted in current speed having little effect on detection efficiency. Tilting of the tethered moorings is indicated as a major limitation on detection efficiency. We propose a new mooring design so that the flotation also generates lift in order to hold receivers in a stable position above the bottom and thereby improve the utility of acoustic fish tracking in fast currents.