Climate change together with increasing demand for space pose a challenge to energy and food production at sea areas. Co-location of offshore renewable energy production, aquaculture and other blue economy activities can answer the need for more sustainable marine space utilization while reducing and dividing costs of the different activities. This paper presents a case study of a multi-use platform that combines wind energy and fish farming in the Gulf of Bothnia, where the sea freezes every winter. A marine spatial planning (MSP) tool is used to find suitable locations for the multi-use platform with respect to economic potential of energy and nutrient production, structural solutions and environmental impact. The tool is used to visualize site selection criteria based on geographic information system (GIS) data such as seabed data, wind and wave data and ice data as well as protected marine areas. Production potential scenarios for the multi-use platform at different scales are calculated. Synergies of combining offshore wind energy and fish farming are discussed.