Studies on Gull Lake, Michigan

Summary Evidence is presented, from studies on deoxygenation of the hypolimnion and from examination of the diatom frustules in a surface mud core, that Gull Lake is becoming progressively more fertile. This appears to be a recent phenomenon, having begun in the last century. Phosphate is identified, from bioassay experiments, as the key nutrient limiting to algal growth. Probable future changes in the lake are discussed, and the existence of `natural' eutrophication is denied.