Progeny from inlet-spawning cutthroat trout (Salmo clarki) in Yellowstone Lake move downstream and progeny from outlet-spawning adults move upstream to enter the lake to rear. I examined the role of genetic control, rheotactic acclimation (acclimating swim-up fry to water current and no water current), constant and fluctuating water temperatures, and changing water source in directing migrations of Yellowstone Lake fry by testing them in simulated stream channels.