The Belgian region of Wallonia said on Thursday that tonnes of fish were killed in a river by pollution that flowed across the border from France and accused the French authorities of being too slow to issue a warning.
The Belgian region said the problem was caused by a leak at a sugar beet refinery, although the French company said there was no proven link between the dead fish in Belgium and the leak at its facility.
Wallonia, which abuts the border with France, said 50-70 tonnes of fish died in its territory along a 36 km (22 mile) stretch of the Scheldt river, also known as the Escaut, and that France's slow response had compounded problems.
The French environment ministry did not immediately respond to a request for comment.
French sugar maker Tereos said a leak had been found on April 9 in a 100,000 cubic metres settling pond at its factory in Escaudoeuvres in northern France, which lead to the spill of waste water into a tributary of the Scheldt.
"Wallonia was not been warned by France. It is important to understand why and above all, do things differently in the future," Wallonia Environment Minister Celine Tellier told Reuters, adding that a polluter could be fined of up to 1 million euros ($1.1 million) in Wallonia.
The Scheldt runs from northern France to the port of Antwerp in northern Belgium, Europe's second largest seaport.
Tereos said the rinsing water leak was repaired on April 10 and river's water quality was back to normal by April 13 on the French side of the Scheldt after aerators were installed.
"At this stage, it is impossible to establish a proven causal link between the incident at Escaudoeuvres in France and what is reported from the situation in Belgium with large-scale fish mortality," the company said in an emailed statement.
The company did not immediately respond to an emailed request for comment on whether any fish had died in the French section of the river as a result of the leak.
Sugar beet residues are rich in organic matter and can drive down oxygen levels in rivers, France's Biodiversity Office says.
The Belgian region of Flanders, further downstream, was also affected but less severely, a spokesman for the regional environment minister said.
Paul-Olivier Delannois, the mayor of Tournai in southern Belgium, through which the river runs, complained in a letter to French President Emmanuel Macron. "France had the information for some time and did not transmit it and that is unacceptable," he said.
($1 = 0.9195 euros)
(Reporting by Marine Strauss in Brussels and Sybille de La Hamaide in Paris; editing by Richard Lough)
