The inflow of 238Pu and 239+240Pu from the Vistula River catchment area to the Baltic Sea

► We estimated plutonium inflow from the Vistula River catchment area to the Baltic Sea. ► We found differences in Pu activities depending on season and sampling site. ► The highest amount of 239 + 240Pu was transported in spring and the lowest in summer. ► Annually, the southern Baltic Sea is enriched with 89.0 MBq of 239 + 240Pu. ► Enhanced Pu amount in water came from snowmelt, rainfalls and leached materials.