After a fish kill in the Oder, current water samples in Poland are unpolluted according to the local environmental authority.
"The current results confirm no presence of toxic substances, including mesitylene, on the entire section of the river examined, which extends over five voivodeships," the agency said on Twitter on Thursday.
The water of the Oder is examined daily.
The death of fish in the Oder had worried anglers and authorities in Brandenburg on the border with Poland in the past few days.
Thousands of dead fish were discovered in the river, some of them near the city of Frankfurt (Oder) and surrounding towns.
According to reports in the Polish media, anglers had already found dead fish on the bank in Poland at the end of July.
According to the authorities, there are now thousands found, first in Lower Silesia, but now also in the Lubuskie Voivodeship further north.
Public prosecutors are investigating environmental crimes
According to the reports, inspectors from the water authority in Lower Silesia had already taken water samples from three places at the end of July.
At the beginning of August, the water authority in Wroclaw announced that the high oxygen content in the water deviated from the typical oxygen concentrations in summer.
It is possible that a substance with strong oxidizing properties got into the water.
In addition, the toxic substance mesitylene was detected in two places.
The local public prosecutor's office is investigating a possible environmental crime.
In Poland, criticism of the authorities' handling of fish deaths is growing.
“The river shouldn't have been used by anyone for 14 days.
But no office has warned the public about this problem,” Polish Green MP Tomasz Anisko wrote on Facebook.
No one has alerted the population that it is forbidden to catch and eat fish, bathe in the river or water animals.
This shows the total helplessness and irresponsibility of state institutions, Anisko continued.