Recently, much concern has been devoted toward the continual deterioration of water quality in the natural lakes of the United States. Carlson (1977) has compiled a trophic state index for lakes based upon chlorophyll a concentration. Gannon (in correspondence) has applied this index to 44 lakes in northern Michigan and has concluded that although most of the larger lakes do receive some effluent from septic tanks, in general those lakes with a relatively large flow and quick turnover are not in any immediate danger. For example, he considers Douglas Lake, Cheboygan County, to be in a state of mesotrophy with ca. 6 micrograms/liter of chlorophyll a. Bazin and Saunders (1971), on the other hand, considered a gradual increase in the rate of oxygen depletion below the thermocline to be an indicator of eutrophication. They detected an apparent trend in Douglas Lake of a more rapid depletion rate. They, therefore, concluded that Douglas Lake is slightly eutrophic. Regardless of whether we consider Douglas Lake mesotrophic or slightly eutrophic, we should be concerned with the possible effects of continued (especially increasing) eutrophication upon the physical and biological aspects of the lake. Before these effects can be adequately understood, one must have a thorough description of the physical and biological components of the lake. Personnel at the University of Michigan Biological Station (UMBS) have been studying Douglas Lake for nearly 70 years, and a considerable amount of data has been compiled. For example, the morphometry of the lake has been described by Scott (1921), Welch (1927), and Wilson (1945). Gannon & Brubaker (1969), Gannon & Fee (1970) and Tallman (1975) have described the seiches and circulation in the lake. The biota, however, have not received such thorough treatment. Moffett (1943) and Neel (1948) studied the biota of Big Shoal, concerning themselves mostly with invertebrates and non-vascular plants. Other individual groups have been examined in the lake. Tucker (1957) worked on the ecology of phytoplankton, and Reighard (1915) studied habitats of the fishes. Published studies on the aquatic flowering plants include Bromley (1967) on the spreading of aquatic flowering plants in deep water, Williams (1970) on the morphology of the water lilies (Nymphaea), and Weber (1972) on the importance of turions in Myriophyllum reproduction. However, no comprehensive list of either the flora or fauna has been published for Douglas Lake. It is our objective to prepare such a list for the aquatic vascular plants.