“We have never had an operation of this magnitude on a river before,” Monika Nowakowska-Drynda of the national fire department press office told AFP. She confirmed that around 100 tonnes of dead fish had been recovered since Friday. The cause of death is uncertain, but authorities suspect chemicals.
“Huge amounts of chemical waste were probably dumped into the river with full knowledge of the risks and consequences,” Polish Prime Minister Mateusz Morawiecki said last week.
The Polish Minister of the Environment, Anna Moskwa, however, clarified on Tuesday that “none of the samples tested so far has shown toxic substances”.
The government is also exploring possible natural causes, according to the minister, including an excessive concentration of pollutants and salt caused by low water levels and very high temperatures.
And a third possibility: the dumping of waste water containing a high level of chlorine by industries, she noted.
Water samples are being tested in Poland and Germany and have also been sent from Warsaw to laboratories in the Czech Republic, the Netherlands and Great Britain.
The first reports of mass fish kills in the Oder came from Polish locals and anglers as early as July 28.
German authorities accused Polish authorities of not informing them of the deaths, and were taken by surprise when the wave of lifeless fish appeared. In Poland, the government has come under fire for not taking swift action. In recent years, the Oder was known to be a relatively clean river, with around 40 species of fish living there.
According to Ms. Nowakowska-Drynda, more than 500 firefighters are involved in the cleanup action.