Lake Arendsee is a dimictic lake with a surface area of about 5 km² and a maximum depth of about 50 m. Due to the input of untreated sewage rich in P the lake turned to eutrophic state in the 1950s. Sediment cores were taken by different methods: short cores (0–50 cm) with a gravity corer, long cores (0–160 cm) with a piston corer. The sediments were sliced into subsamples under argon atmosphere in a glove box. The samples were analysed by ICP-OES and ICP-MS on main and trace elements after digestion in either aqua regia or HF-HNO3-HClO4. Analogous cores were dated by varve counting and radiometric methods. The enforced build-up of industry and agriculture since the 1950s is displayed in the sediment composition. The P concentrations increase from a background of about 600 ppm (oligotrophic state of the lake) to more than 4,000 ppm in a depth of 14 cm, which corresponds to the 1970s. In 1976, a hypolimnetic withdrawal and a sewage plant were built. Above the corresponding depth the concentrations of P and heavy elements decrease in the sediments but are still by far higher than the background values. The bonding form analyses document mineral equilibration by diagenetic processes. Stable sulfidic bonding forms become predominant with increasing depth.