This study examined the vertical distributions of total phosphorus (TP) and phosphorus fractions, and the iron and organic matter, in the littoral sediment in a macrophyte-dominated, clearwater state in Lake Mogan between September 2005 and August 2006. Benthic macroinvertebrates and total bacteria in the sediment also were determined. No clear seasonal or depth-related (0-20 cm) patterns were found in sediment concentrations for the measured parameters. The phosphorus release was quantitatively very low, and a negative phosphorus release (-0.132 μg m -2 day -1 ) was measured during the summer months. The TP concentrations of the sediment samples ranged between 675.00 and 1463.80 μg g -1 dry weight (DW), and the trophic level of the lake was eutrophic. On average, inorganic phosphorus fractions comprised the largest fraction (63%), while organic-bound phosphorus (Org ≈ P) constituted 37% of the TP in Lake Mogan. The most important phosphorus-immobilizing factors are high iron content (14 200-47 750 μg g -1 DW), the sediment's clay content (47.80-51.80%), and an abundance of macrophytes at the sampling station. The low abundance of benthic macroinvertebrates (510-850 individuals m -2 ), which depend on sediments with high iron and low organic matter (5.42-13.30%), played a role in the sediment phosphorus retention. Although bacterial abundance in the surficial sediment appeared to be positively correlated to temperature, the overlying water did not experience anoxic conditions, supporting a state in which bacteria were able to retain phosphorus in their cell structures. Long-term changes in the sediments of Lake Mogan must be monitored lake. In order to optimize the management of the lake, and to determine the longevity of a clearwater state following management measures and continued external phosphorus loading, long-term changes in the sediments of Lake Morgan must be monitored.