None of the studies conducted have confirmed the presence of toxic substances that reportedly caused the death of tons of fish in Oder river, Polish Minister of Climate and Environment Anna Moskwa said on Sunday.

Over the last two weeks, thousands of dead fish have been found in Oder, which runs between Poland and Germany, with both countries warning of an ecological disaster.

During a joint press conference with German Federal Minister for Environment, Nature, Nuclear Safety and Consumer Protection Steffi Lemke, Moskwa said that such a scenario could not be ruled out even if no toxic substance has been found so far.

Moskwa, Lemke and other officials from both countries held meetings Sunday in the Polish city of Szczecin, which is situated next to the border with Germany, to discuss the environmental issue.

The Polish minister also said that by the decision of Prime Minister Mateusz Morawiecki, a team had been made over the contamination of Oder, while crisis management staffs were operating at province level as well.

Morawiecki reiterated on Saturday that the government would "do everything to limit losses and minimize the negative effects of the Oder pollution" and that those responsible would be punished. According to Morawiecki, there could probably be a discharge of harmful substances into Oder.

The head of Poland's National Water Management Agency and the chief inspector of the country's Environmental Protection Agency have been sacked over the matter.