Why did so many fish die in the Barnai River?

A sudden chemical imbalance in Bangladesh’s Barnai River killed large numbers of fish, leaving villagers and local fishermen alarmed. Ammonia levels rose to 1.5 milligrams per litre, compared with about 0.25 milligrams under normal conditions, while oxygen levels dropped below acceptable limits.

Dead fish began floating to the surface along the Natore stretch of the river on Thursday night and Friday. Most were smaller local varieties. No more floating fish had been seen since Saturday, but authorities continued investigating what caused the rapid deterioration in water quality.

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The water had turned dirty and foul over the last few weeks, making it difficult to catch fish.

“The water had turned dirty and foul over the last few weeks, making it difficult to catch fish,” said Bhobesh Chandra, a fisherman from Boshila village in Naldanga. He suspected that the worsening water quality had caused the deaths.

The Natore District Fisheries Office formed a three-member committee on Sunday, consisting of three upazila fisheries officers. The committee collected water and fish samples, and chemical tests confirmed that oxygen levels had fallen rapidly while ammonia had risen sharply.

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The probe committee has already collected water and fish samples from the river for testing. Chemical examinations revealed that oxygen levels decreased rapidly while ammonia levels spiked abruptly, causing the mass death of fish.

Fisheries Officer Md Omor Ali said rotting jute around nearby beels and riverbanks may have released large amounts of organic waste into the water. He also cited the continuing discharge of untreated industrial waste and poultry farm runoff as further sources of deterioration.

Conditions have begun to improve as cloudy weather clears, sunlight returns and water flow increases. Authorities are warning riverside residents against polluting the water and urging them to help protect aquatic biodiversity. The committee is expected to submit its findings within three days, after which action will follow its recommendations.

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The situation is now improving as the cloudy weather clears, sunlight returns, and water flow increases in the river.