Mystery on the Oder after the death of thousands of fish

Scientists are investigating the cause of a ‘catastrophic’ mass fish kill in the Oder River between Poland and Germany, the Guardian has reported. Polish scientists have traced high levels of salt, but dismissed German claims of mercury pollution, with both governments suspecting an untraced chemical spill. German authorities have banned fishing and swimming in the river. Some 2,000 police, 300 firefighters and 200 soldiers were deployed to remove the carcasses.