Since July, more than 100 tonnes of dead fish have been pulled from the River Oder in Germany. The deaths have remained a mystery until now, with scientists suggesting that toxic algae could be the cause.

Toxic algae thought to be the cause of deaths in the Oder

Scientists believe they may have found the reason why so many fish perished in the Oder River over the past few months. Satellite imaging has revealed high levels of chlorophyll in the water, something which suggests the presence of algae. Poland’s deputy environment minister seemingly confirmed this on Twitter: “The examinations conducted so far have confirmed the presence of toxic algae (Prymnesium Parvum).”

According to German environment ministry spokesperson Andreas Kübler, the formation of these algae, known as “golden algae”, is not a natural phenomenon, as the algae does not usually bloom to the extent it has under natural conditions. Kübler explained that the algae probably developed due to the high levels of salt in the water.

High levels of pesticides found in river

Kübler suggested that several organic and inorganic substances may also be responsible for the deaths, according to tests. The environment ministry in Brandenburg has reported high levels of pesticides in the water, which may have contributed to the high salt levels in the water. Polish Prime Minister Mateusz Morawiecki has also suggested that chemical waste may have been responsible.

However, Poland’s Climate and Environment Minister Anna Moskwa has refuted these claims and has said the government is looking into possible natural causes, which may have resulted from recent high temperatures and low water levels. Moskwa has since warned on Twitter against “fake news from Germany.”

Poland’s water authority has also reported 282 unauthorised flows of wastewater into the river. German authorities have accused the Polish of not warning them of the problem early enough.