During summer (May-October), a positive relationship was evident between lake water levels and chlorophyllaconcentrations in littoral and littoral:pelagic interface regions of Lake Okeechobee. High water levels in synergy with the large size (1830 km2), shallow depth (Zx= 2.7 m), and unique bottom configuration of Lake Okeechobee appeared to facilitate greater horizontal mixing and circulation which resulted in higher phosphorus concentrations in a portion of the littoral zone. In shallow littoral regions where light penetration was sufficient, an empirical link between phosphorus and chlorophyllawas evident. East-to-west and north-to-south gradients of phosphorus extended from hard-bottom littoral regions to the open-water pelagic zone located over soft, phosphorus-laden flocculent muds, and these gradients were more pronounced at low lake levels. Phosphorus loading from tributaries only affected algal concentrations in a small portion of the lake. A higher water level regulation schedule was implemented in 1978 to augment water supplies and this increased lake levels when precipitation was sufficient. A slightly lower lake level regulation schedule might reduce the frequency of hypereutrophic algal blooms in nearshore and littoral areas.