The fish deaths happened on a 20 kilometre-river section which runs through many communes in Ba Thuoc District.
The dead fish on Ma River
Among the figure of 6.5 tonnes, fish raised in cages accounted for some 4.5 tonnes, while the remainder is natural fish and shrimps.
Local authorities took fish samples for testing.
Meanwhile, local people suspected that the fish deaths were due to environmental pollution caused by wastewater discharge.
Initially, farmers were instructed to temporarily remove their fish cages out of the affected area.