Discharges from the Polish mining industry apparently caused fish deaths in the Oder last summer. According to a report published by Greenpeace on Wednesday, scientists were able to detect salt discharges in three tributaries of the Oder in the Silesia region.

Accordingly, three mines of the mining companies Polska Grupa Górnicza and Jastrzebska Spólka Weglowa (JSW) are responsible for this, which operate mines there. Downstream, salinity rose sharply, according to the report.

JSW said on Friday on request that it adheres to all provisions and regulations of the Water Act. The salinity in the Oder is constantly monitored at the height of Krzyzanowice. JSW is majority-owned by the state.

Mining industry under suspicion for some time

The company admitted that saline mine water was collected via the so-called "Olza collector" and then led into the Oder in a controlled manner via nozzles on the riverbed. In addition, mine water is also introduced into the Oder tributary Bierawka. This is done in a way that is safe for the environment, it said.

In July and August, fish and mussels died in the Oder over a length of 500 kilometres due to a toxic algae. Hundreds of tons of fish had to be recovered. The brackish water algae was able to spread, especially due to the high salinity of the river.

For some time, the wastewater of the mining industry had been suspected of having caused the disaster. So far, however, it was unclear where the salty water came from.

The report by the german-Polish Greenpeace team is based on water samples from August, November and December. The Leibniz Institute of Freshwater Ecology and Inland Fisheries had already published a report at the end of November, according to which the river continued to have too high salinity.