[en] Waters from the Skagerrak Sea entering the system of fjords inside Farsund in the southern tip of Norway (including Lyngsdal, Hellvik and Framvaren fjords) contain plutonium derived from European nuclear fuel reprocessing facilities in the United Kingdom and France, as shown by the ²³⁸Pu/^239,240Pu activity ratios measured for water samples from Hellvik and Framvaren fjords. The shallow sills interconnecting this series of fjords, however, severely restrict water exchange. Thus, at the northernmost Framvaren fjord (connected to Hellvik fjord by a 500-m channel of 2 m depth), the ²³⁸Pu/^239,240Pu signature for Pu derived from fuel reprocessing is found only in the surface layer (upper 20 m) while global fallout Pu ratios are observed in the permanently anoxic zone of this fjord. Plutonium oxidation state measurements in waters collected from Hellvik and Framvaren fjords show that water exchange occurs between two basins by a process of interleaving, with subsequent reduction of oxidized Pu species as these reach the anoxic zone. Plutonium serves as a useful tracer for water exchange between these fjords and the Skagerrak Sea. (author)