Thousands of dead fish have washed up hundreds of kilometers of the river since last month.

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A toxic substance is believed to have contaminated the water, although the exact chemical is still unknown despite testing.

The German government asked people to avoid the river and warned of an environmental disaster.

However, activists alleged that the authorities in both countries did not work together and did not respond quickly to the disaster to protect the people.

Last Friday, Polish Prime Minister Mateusz Morawiecki fired two environmental officials over their handling of the incident.

Morawiecki explained that initially the problem was only considered “local”, but it soon became “much bigger”.

The prime minister added that it would take “years” to recover the river.

Morawiecki noted that “huge amounts of chemical waste” have been dumped into waterways without considering the risks to wildlife.

German Environment Minister Steffi Lemke said there would be a thorough investigation into the incident and that authorities were working “at full speed” to find the cause.

Home to dozens of species

Polish fishermen began reporting problems on July 28, after tons of dead fish were pulled from the river.

The Oder is considered a clean river and is home to 40 species of domesticated fish, reports the AFP news agency.

However, an official from Germany’s Brandenburg state said test results showed elevated oxygen levels in the water, indicating the presence of a foreign substance.

Beavers, birds and ducks were also affected, said Katarzyna Kojzar, a journalist with the Polish investigative website OKO.press.

The possibility that the Oder River is contaminated with mercury is worrying, Kojjar told the BBC.

But she noted that there is still no confirmation of the substance, its origin, or whether it has had any effect on humans.

“We knew it was serious, but we didn’t know what it was,” Kojjar said.

Dredging work in the river may have released the combined mercury, a fisheries researcher told German broadcaster Deutsche Welle.

But Christian Wolter of the Leibniz Institute said the combination of historically low water levels in the Oder and a heat wave already signaled that the fish were in trouble.

This text was originally published by https://www.bbc.com/portuguese/internacional-62543763