Hundreds of dead fish have been found floating in Halda River and its adjacent canals since Tuesday due to pollution of the river water. Bangladesh Fisheries Research Institute (BFRI) sources said the level of ammonia in the water has risen above the tolerance level of aquatic species and the level of dissolved oxygen has fallen, leading to the death of around 20 species of fish. Researchers from BFRI, Halda Research Laboratory of Chittagong University (CU) and the environment department have collected dead fish and water samples from different points of Halda River and its adjacent canals to find out the possible reasons for the deaths.

Hathazari upazila fishery officer Md. Azharul Alam told The Independent: “We suspect there are four causes of pollution in Halda. These are industrial water getting mixed with the river water, excreta from poultry farms set on the river banks may have fallen into Halda, toxic water from adjacent bazaars may have flowed in with rain water and toxic wastes released by Asian Paper Mills.”

“The maximum number of dead fish was found on Wednesday. These deaths were reported from four points of Halda River—Purali Khal, Madari Khal, Khandakia area of Madhunaghat and Katakhali area. Due to the recent heavy rain, toxic waste from the four mentioned sources might have mingled with the river water, leading to it being polluted,” he added.

“We are testing the river water and dead fish to identify the reasons. It will take four to five days for the report to come in,” he said.

Since Tuesday, at least 20 species of fish including mrigal, catla, ruhi, prawn, long-whiskered, tilapia and kuchia have been found floating in Halda.

Halda is the country’s lone natural fish spawning centre. Every year during the Bangla months of Baishakh and Jaishtha (April and May), different indigenous species of carps like catla (Catla catla), ruhi (Labeo Rohita), mrigal (Cirrhinus Marigala) and kalbaoush (Labeo Calbasu) start migrating to the spawning ground of Halda from rivers like Karnaphuli, Matamuhuri and Sangu. This year, the collection of eggs was 22,680 kg, the highest in the last 10 years. This is because the government has taken several steps to save Halda and restore it as a natural breeding ground for fishes. In 2016, there was no collection of eggs, while it was a mere 1,680 kg in 2017.

Manzoorul Kibria, professor of zoology at Chittagong University and Halda River Research Laboratory coordinator, said, “Due to the tide in the river on Saturday, the situation is improving. We did not think of such massive pollution of Halda. This disaster reminds us that we have to take more action to save Halda immediately.

“Earlier, we thought that only one point that is Khandakia was vulnerable. Now, three more points—Purali Khal, Madari Khal, and Katakhali—have emerged,” said Kibria. Halda, which covers a 40-km-long stretch from Nazirhat to Kalurghat has been declared as a sanctuary of the broad fish. Halda River wears a festive look every year when hundreds of fishermen start collecting fertilised eggs released by the broad fish.