The inflow of 238Pu and 239+240Pu from the Odra and Pomeranian rivers catchments area to the Baltic Sea

► We estimated plutonium inflow from the Odra 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. ► Annually, the southern Baltic Sea is enriched with 45.86 MBq of 239+240Pu. ► Enhanced Pu amount in water came from snowmelt, rainfalls and leached materials.