The release of nutrients from the sediment into the water column, i.e. internal nutrient loading, is an important problem in the restoration of eutrophied lakes. The ebullition of gases, mainly methane, has been identified as the key process in nutrient transportation in the internal loading. We studied whether methane production in lake sediment and the release of nutrients into the water column could be prevented by the addition of gypsum (CaSO4 x 2H2O). Three different gypsum products were examined in a controlled laboratory microcosm with a continuous water flow. The addition of gypsum (especially Fe-gypsum) into the sediment increased the redox potentials and reduced methane production and release of phosphorus from the sediments during an incubation period of 3 months. Gypsum evidently acted as a slow-releasing source of sulphate in sediment, which likely enhanced the activity of sulphate-reducing bacteria and improved the overall mineralisation rate of organic matter. The liberation of H2S and phosphate, which might be an undesired consequence of increased sulphate reduction rates was prevented by the application of Fe-containing gypsum likely as a result of the formation of pyrite and apatite minerals.