Masses of dead fish were found in the Oder River, which runs along the border between Poland and the Czech Republic, according to the Polish authorities.

Tissue and water samples are now planned after some 30 kilogrammes of fish were recovered near the village of Chałupki, the authorities said on Tuesday evening.

The fish were found over several days and appeared to have drifted downstream from the part of the Oder river on the Czech side of the border.

The dead fish were suspected to have died off in Oder in the summer of 2022 between Poland and Germany.

After extensive analysis, scientists concluded that the toxic bloom of the rare golden algae Prymnesium parvum likely caused deaths last year. 

(dpa/NAN)