The northern extension of the Baltic Sea, the Gulf of Bothnia, is a weakly stratified sea. One would therefore expect that the deep water of the Gulf is easily renewed through deep thermal convection, or even through deep haline convection, as the Gulf is more or less covered with ice every winter. However, the present study shows, through analysis of historical temperature, salinity and density data, that the deep water in the Gulf of Bothnia is mainly renewed by major inflows of Baltic Proper surface water. The penetrating water forms a dense bottom current in the Gulf. In the southern part of the Gulf, the Bothnian Sea, the volume flow of the bottom current is found to increase by 10%. It is therefore not likely that the bottom current properties are changed to any appreciable extent. The bottom current properties in the Bothnian Bay, on the other hand, are highly affected, as the volume flow is estimated to increase by 150% in this basin.