Studies of sub-surface current patterns in South Fishtail Bay, Douglas Lake, were initiated in August, 1964 and continued May through August, 1965 and 1966. In spite of the volume of research conducted on Douglas Lake through the UMBS, no previous research primarily concerned with hydromechanics has been published. Incidental to biological studies, limited information on water movements was obtained in the vicinity of South Fishtail Bay by Moffett (1943) and Neel (1948). Douglas Lake is noted in the literature for its depression individuality with each basin in the lake acting separately in terms of their physical, chemical, and biological characters. South Fishtail Bay, the basin most protected from prevailing winds, has the shallowest epilimnion and the coldest bottom water. This indicates that mixing of wind-generated currents is not as strong in South Fishtail Bay as in the rest of the lake and that the bay stratifies earlier than the other depression, thereby isolating the hypolimnion from circulation before it warms up appreciably.