A limnological survey of Grand Traverse Bay in northern Lake Michigan was conducted on 30-31 July, 1954. The physical character of the bay is described including a brief account of the physiography and soil types of its drainage basin, A detailed bathymetric chart of the bay has been prepared, as well as a compilation of morphometric data concerning its area and volume. The results of bottorn sediment analyses are reported and discussed. The surface and subsurface distributional patterns of several parameters including water transparency, temperature, and dissolved silica and magnesium are described. Based on a consideration of all available information, including limited drift bottle recovery data, the principal water circulation pattern in the bay has been deduced as follows: Water entering Grand Traverse Bay from the Lake Michigan basin flowed around Lighthouse Point into the northwestern part of the embayment. This current was, in part, directed to the west shore in the vicinity of Northport and Sutton Bays and sank there. A small portion of the inflowing water was deflected into the East Arm, but the main current flowed into the West Arm where the surface waters were directed on-shore south of Bowers Harbor and sank. A subsurface return flow along the mid-depths of the West Arm basin was the source of water which upwelled in a large elongate eddy located near the east shore at the mouth of the bay. The surface current pattern in the East Arm was a complex of two eddy formations. Lake Michigan water was apparently being fed slowly into this complex along the shore of Old Mission Peninsula. Water escaping from the complex flowed northward along the east shore into the counter clockwise rotating eddy at the bay mouth. There was apparently little deep current activity in the East Arm other than an extension of the mid-depth outflow from the West Arm which extended part way down the East. The East Arm appeared to have fiord-like characteristics not found in the West. No evidence of stagnation was found in either arm.