Poland says Oder tests so far not showing poison as cause of fish die-off

Tonnes of dead fish have been found since late July in the river Oder, which runs through Poland and along the border with Germany.

Both countries have said they believe a toxic substance is to blame, but have yet to identify what it is.

"As of today, none of these (water) tests have confirmed the presence of toxic substances," Moskwa said after meeting with her German counterpart Steffi Lemke and other German and Polish officials in Poland's Szczecin.

Moskwa said samples are now being tested for the presence of pesticides and around 300 more substances will be checked for in the coming hours.

She said Polish authorities were working to identify how the unidentified substance that caused the death of the fish had entered the river.

Lemke said the extent of the damage to the ecosystem and how long it would last was still unclear, and the Polish and the German sides would work together on the clean-up, investigation of the cause and improving communication to prevent future disasters.

Green activists and opposition politicians have criticised the Polish government for not responding quickly enough to the danger and failing to alert Poles to avoid bathing and angling in the river.

Germany has also grumbled over Poland's response. Lemke said the Polish and German sides agreed at their meeting "one of the most essential points" in a similar situation was that all relevant organisations and authorities could get quick and comprehensive information.