We tested the performance of low- (40 MHz) and high-frequency (150 MHz) radio and ultrasonic (75 kHz) telemetry transmitters in Robert S. Kerr Reservoir, Oklahoma, a polyhaline body of water. We measured the maximum detection distance of all 3 transmitters at various depths and conductivity levels in lacustrine habitats and the ultrasonic transmitter in riverine habitats. The ultrasonic transmitter had the greatest detection distance (600-1,200 m) in all lacustrine habitats and in clear, deep riverine habitats. Ultrasonic transmitter detection distance decreased by 94% at a shallow riverine site with high velocity and suspended sediment levels compared with a moderately deep, clear riverine site. Maximum detection distance for the low-frequency radio transmitter was 370 m at a depth of 1 m. It was nearly undetectable below 1 m at conductivity levels above 345 jxS/cm. The high-frequency radio transmitter had a detection distance of up to 390 m at the surface and was virtually undetectable when in water deeper than 1 m. Considering the performance of the 3 types of transmitters, we recommend using ultrasonic transmitters for telemetry studies of highly mobile fishes in reservoirs that encompass a wide range of conductivities and have depths greater than a few meters. However, for studies of fishes restricted to shallow rivers with high suspended sediment loads, low- or high-frequency radio transmitters may be preferable to ultrasonic transmitters because of their greater detection distance under these conditions.