An echo sounding device coupled with a differential GPS was applied for a spatial survey of the shallow Spremberg Reservoir to characterize areas of similar sediment composition and phosphorus (P) mobility to help elucidate its influence on water quality. Forty three intact sediment cores were taken to determine dry weight (DW) and total P. Four areas were differentiated based on the sonar and dry weight data. From each of the areas, specific surface area, P sorption characteristics and P pools by means of a sequential P extraction as well as the total and diagenetically reactive iron were determined. A high P sorption capacity of up to 7.4 mg P g^-1 DW could be determined at up to 180 mg Fe g^-1 DW and high proportions of iron-bound P in the surface sediment. The P release rates calculated from pore water profiles were extremely low. The high P binding capacity, the low P mobility and the short water residence time have favoured the improvement of water quality in recent years.