Photo: NewsLubuski/East News Polish soldiers pick up dead fish from the Oder river near Krosno Odrzanskie on August 12, 2022 in western Poland near the German border. In recent days thousands of dead fish have been found in various parts of the second largest Polish river - Oder. Polish authorities are trying to establish the source of the possible toxic pollution, which kills not only fish but other water animals i.e. beavers. On a stretch of almost 200 kilometres, Oder is a natural border between Poland and Germany.