An analysis of the water from Monday showed evidence of synthetic chemical substances, very probably also with toxic effects for vertebrates, the ministry said on Thursday. It remained not clear how the substance entered the water.
The state laboratory found high levels of mercury in the water samples, according to local broadcaster RBB.
According to the head of Poland's national water management authority, the presence of mercury in the water had yet to be confirmed, according to a private broadcaster, Polsat News.
These are press reports at the moment. The head of Polish waters, Przemyslaw Daca, said there was no confirmation regarding mercury in the Oder.
The ministry in Brandenburg, the state of Berlin, said it had not yet been able to assess how many fish had died in Poland and Germany. The chains of communication between the Polish and German sides did not work in this case, according to Brandenburg Environment Minister Axel Vogel, adding that German authorities still had no notification from Poland about the incident. Germans in the Uckermark and Barnim districts, home to rolling hills and a nature reserve, warned citizens not to contact with water from the Oder and an adjacent canal in a warning sent to the public earlier this week. Dead fish are removed from the Polish side of the Oder River on Saturday. Fish are removed from the Oder River on Saturday. Since late July, tons of dead fish have been found in the Oder River. Polish Prime Minister Mateusz Morawiecki said the waterway would take years to return to normal. The pollution is very large. Morawiecki said in a regular podcast on Friday that the Oder may take years to return to a normal state. He said it was likely that enormous amounts of chemical waste had been dumped into the river, and that those responsible would be held accountable. On Friday, Morawiecki fired the head of Poland's national water management authority, Przemyslaw Daca, and the head of the general environmental inspectorate Michal Mistrzak, saying that their institutions should have reacted earlier. Poland plans to set up a barrier on the Oder near the city of Kostrzyn to collect dead fish flowing down the river, with 150 territorial Defence Forces soldiers delegated to help with the clean-up.