Sockeye underyearlings at Babine Lake. B.C. were observed to undergo diel vertical movement from July through to October 1967. This movement was more pronounced in August when the lake was most distinctly thermally stratified. The presence of a sharp thermocline (about 8 °C in 10m) did not appear to impede their movement in any substantial way. By day, the sockeye inhabited cold (5-6 °C), deep (35-55 m) water and at night the warm water (about 16 °C) of the epilimnion. Vertical movement was closely associated with change in light levels.