We used the rate of change in oxygen concentration in the hypolimnion as an index of biological productivity during the early summer. An increase in biological production in the surface depths of the lake should result in a greater amount of particulate organic matter settling into the aphotic hypolimnion. Decomposition of this organic matter will result in a higher absolute rate of oxygen consumption in the hypolimnion. The estimated rate of consumption of oxygen in the hypolimnion was therefore used to determine whether or not the lake has been undergoing change during the last 45 years and to develop some predictions concerning what might happen to Douglas Lake in future years. ...Thus it is possible that the above combination of long term effects, both decreasing and increasing in intensity, could have produced the trend of increasing hypolimnetic oxygen depletion in Douglas Lake. The major removal of forests from the region may have initiated a dramatic and long-term change in the productivity of Douglas Lake. As the effects of deforestation lessened, subsequent events of lesser intensity may have served to prolong and increase the initial changes. Since this apparent eutrophication has occurred in what would be considered as a relatively undisturbed lake, it suggests that small but prolonged changes in the environment have caused rather significant changes in the intensity of metabolism and productivity of Douglas Lake. It also suggests that it might be appropriate to initiate rather detailed and long term studies on Douglas Lake and its drainage basin in order to analyze and to evaluate more specifically the nature of small environmental changes and their effects on such a lake.