The event is reminiscent of last summer’s environmental disaster in which an estimated half of the Oder’s fish population died following poisoning caused by the toxin-producing golden algae.
On Thursday, Environment Minister Anna Moskwa reassured Poles that the river is safe.
“We have experience, and we don't want this disaster to be repeated either in the Czech Republic or in Poland,” Moskwa said.
“The Czechs claim that low oxygen levels might be the cause… Anyway, on the Polish side, the Oder is safe,” she added, noting that “the water parameters are secure, posing no threat and showing no resemblance to last year's situation.”
Click on the audio player above for a report by Radio Poland’s Michał Owczarek.