BERLIN, Aug. 15 (Xinhua) -- The cause of a mass fish die-off in the River Oder which runs through Germany and Poland is still unclear, officials said on Monday.
"We do not know yet what exactly has caused the poisoning-like symptoms in the fish," said Dietmar Woidke, minister president of the federal state Brandenburg, at a press conference at the scene. Authorities are working hard to establish the cause and to remove the carcasses, he said.
"It is of existential importance for us to know what exactly has happened and whether there is still a danger to people and the environment or whether this danger has perhaps gone with the waves," Woidke said.
Tons of dead fish have been found in the river since late July, which prompted both Germany and Poland to sound the alarm over a potential ecological disaster.
Although water levels are at record lows and water temperatures are high, there were "significantly raised oxygen levels," said Axel Vogel, the environment minister of Brandenburg. This anomaly has remained "unexplained to this day."
The mass fish dying is believed to have been triggered by a yet unidentified substance. Polish officials are in the process of checking the samples for 300 substances in their central laboratory, Vogel said.
Mercury has so far been ruled out as the cause of the disaster, the Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection (BMUV) said on Monday. Detailed findings are to be made available soon.
"We are all united by our great concern about the extent and consequences of this environmental disaster," said German environment minister Steffi Lemke after meeting with Poland's environment minister Anna Moskwa on Sunday.
