Nearly 20 tonnes of fish are believed to have been killed by toxic waste in a Serbian river.
The fish kill has prompted an investigation into what caused the "ecologial catastrophe," officials told the International Herald Tribune.
"A high concentration of ammonia has caused the killing of 20 tonnes of fish in the River Timok," the public health department in the eastern town of Zajecar, some 250 kilometres (150 miles) east of Belgrade.
Water testing analysis showed ammonia levels were up to 1600% higher than recommended. Water samples were taken from Timok, near the spot where sewage from the nearby town of Knjazevac spills into the river.
"The ecological catastrophe" was noticed last weekend, when local fishermen spotted hundreds of fish floating near the banks of the river, apparently dead from a lack of oxygen, Belgrade Radio B92 reported.
However, Serbian ecological inspector Vesna Mitrovic told Tanjug news agency that the results of analysis were yet to show what caused the incident "of massive proportions."
Mitrovic added that the river was apparently contaminated from the local sewage system, which is connected to the industrial zone of the town of Knjazevac.
Expert, Srdan Peric of the local fishermen's association said the waterway would need at least 10 years before it could fully recover from the environmental disaster.
The Timok is a tributary of the Danube which empties into the Black Sea.