Lake Huron was surveyed synoptically three times (28 and 29 June, 27 July, 25 August) during the summer of 1954. In each survey more than 80 stations were occupied. Data obtained included temperature, magnesium, silicon, calcium, and conductivity in both horizontal and vertical distributions. The horizontal distributions of transparency and relative humidity were measured. Drift bottles were released at each station. Computed parameters included surface currents and probable directions of bottom currents. Calculated surface current velocities agreed well with average drift bottle velocities. Two parent water masses, Lake Michigan and Lake Superior waters, and a mixture of the two, Lake Huron water, were present. Lake Superior water could be followed for only short distances either horizontally or vertically. Lake Michigan and Lake Huron waters were both widespread on the surface. The bottom water appeared to be of both Lake Michigan and Lake Huron origin, with Lake Michigan water limited in general to the west side of the lake. Lake Huron water dominated the east side of the lake and was present in varying amounts on the west side. Both bottom water types could be traced well into the southern end of lake. The fundamental surface circulation pattern in the upper and central portions of the lake appeared to be counterclockwise. In the lower end of the lake outflow to the St. Clair River appeared to consist of a meandering surface current, near or east of the midline of the lake, which approached the entrance of the river from the northeast. The surface circulation of the lake appeared to reflect the direction and velocity of the winds of the preceding twelve days. A thermocline was absent in the wide central portion the lake in late June. By July a pronounced thermocline developed over all but the ends of the lake. It was also present in late August. The development of the thermocline interposed a strong density structure between surface water and bottom water. After its formation most upwellings drew water from the thermocline depth or less, and the weaker sinkings did not extend through it. The major wind-induced sinkings appeared to extend into the bottom water despite the development of the thermocline. Warm surface water carried won appeared to contribute heat to the bottom water and possibly to buoy up the thermocline. The circulation of Lake Huron has certain characteristics which are at least pseudo-oceanic and others which are definitely lacustrine.