Despite of extensive water protection measures, the state of the Baltic Sea is poor. Nutrients levels in the water and sediments are high, and anoxic dead bottoms are widespread in the sea floor. Even shallow archipelago waters are suffering from oxygen deficiency, though effective water protection measures have cut nutrient discharges from coastal areas. The phenomenon is supposed to be caused by so called internal loading of phosphorus from sediments. Rough estimations made in an earlier INTERREG IIIA financed project, BEVIS, show that phosphorus fluxes from sediment may equal or even exceed the total phosphorus load from land sources. Even if the effects of the internal phosphorus loading on the water quality are widely recognised, the present water quality models cannot adequately simulate internal phosphorus fluxes. In the SEABED project we will collect sediment data for phosphorus flux estimations in the project area. We will use the data in generating a dynamic sediment-phosphorus model that will be integrated in a water quality model that can simulate quality changes in the archipelago waters. WP1 deals with the project management and coordination. The aim of WP2 is to collect empirical data to quantify fluxes of phosphorus between sediment and water from different sedimentary areas in Svealand, Åland, SW Finland and W Uusimaa archipelagos. Based on the collected data a dynamic sediment-phosphorus model will be constructed and used in the overall modelling work package 3. The aim of WP3 is to develop a joint water quality model for the project area with a more detailed resolution in the archipelagos and a coarser resolution in the open sea areas. Process-oriented modeling dealing with sediment processes and primary production is part of this WP. Results of the modeling work will be implemented in a user friendly model application with different scenario runs developed in WP4. WP4 includes establishing of scenarios with regard to loading sources, climate change and artificial aeration: 1) Effect of the EU WFD programmes, 2) Effect of the HELCOM BSAP, 3) Effect of climate change, 4) Effect of the WFD action plans and the BSAP, taking into account climate change, 5) Effect of eco-engineering measures. WP5 focuses on awareness raising and information campaigns. The results: 1) A joint three-dimensional water quality model for the project area that can simulate water quality changes caused not only by land-based or atmospheric nutrient loading, but also by phosphorus fluxes from sediment to water. 2) New information of the internal phosphorus loading which can also be used in other archipelago areas in Sweden, Åland and Finland. 3) Results of the scenario simulations which can be used in water management plans even in other Baltic coastal areas. 4) Spreading joint information to the decision makers and inhabitants will increase the environmental awareness and the responsibility of the common environment. Achievements: The SEABED project improved the situation in the Baltic Sea by creating tools for the management of the eutrophied archipelago areas with a special focus on the quantification of the internal load of phosphorus. Project enhanced environmental management co-operation between the central Baltic archipelagos and islands and created scenarios about the effects of remedial measures. By using existing and new data from field studies the partners acquired unique knowledge and created a database of the sediment phosphorus resources and potential of internal loading from the shallow‐water archipelago sedimentscreated modelling toolsestablished new regional cooperation and connections among the authorities, managers and other stakeholders within the project area.