< p class="sc-v64krj-0 knjbxw">More than 500 firefighters take part in the clean-up action in the Oder River, where tens of thousands of fish have been found dead.
Polish firefighters said on Tuesday they had rescued 100 tons of dead fish from the Oder River that runs through Germany and Poland, heightening fears of an ecological disaster.
We've never had an operation of this magnitude on a river before, said Monika Nowakowska-Drynda of the National Fire Department press office.
She confirmed that approximately 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 likely dumped into the river with full knowledge of the risks and consequences, Polish Prime Minister Mateusz Morawiecki said last week.
La Polish Environment Minister Anna Moskwa, however, clarified on Tuesday that none of the samples tested so far have shown toxic substances.
Tens of thousands of fish have been found dead in recent days along the Oder River on the border between Germany and Poland.
The government is also exploring possible natural causes , according to the Minister, including an excessive concentration of polluting substances and salt caused by low water levels and very high temperatures.
And a third possibility: the dumping of wastewater containing high levels of chlorine by industries, she noted.
Water samples are examined in Poland and Germany and were also sent from Warsaw to laboratories in the Czech Republic, the Netherlands and the United Kingdom.
The first reports of the mass death of fish in the Oder were made by Polish locals and anglers as early as July 28.
German authorities accused Polish authorities of not having them informed of these facts, and were taken by surprise when the wave of lifeless fish appeared.
In Poland, the government has come under fire for not taking quick action.
In recent years, the Oder has been known to be a relatively clean river, with around 40 species of poi ssons living there.
According to Ms. Nowakowska-Drynda, more than 500 firefighters are involved in the cleanup action.