The natural spawning in the River Halda is in a deep crisis with many fish species becoming extinct.
Currently, 26 out of 76 species of fish are not available in the natural breeding ground because of water pollution through indiscriminate dumping of industrial and solid waste into the river, salinity, sand extraction, sluice gates and dikes built on riverbanks and others.
Of them, at least five species of fish that have become extinct are chital, bani koksa, ghor poia, guijja ayer, and meni or bheda, according to a research by the Department of Fisheries and the Halda River Research Laboratory of Chattogram University in 2009-2016.
The fish species that are now not found in the river are gani chapila, lilsa, telipasa, bani koksa, koti, dhela, chepchela, boali pabda, tengra, shillong, ghaura, batasi, gajra, kaitar poya baila, nona baila, chiring, chewa etc.
The research also found the destruction of fish habitats led to a significant fall in fish egg production.
Dr Md Manzoorul Kibria, professor of the Department of Zoology at the University of Chattogram, said one of the main reasons for the loss of fish species is unplanned sluice gates. The construction of dams also reduced water flow, resulting in the loss of essential food sources, like benthos, for fish species.
From Sattarghat to Madunaghat of the river, the habitat for brood fishes, there is a severe shortage of food sources. The maturation of fish gonad also requires quality water and plenty of food during the breeding season, he added.
Sumon Jaldash, a fisherman of the River Halda, said, "We have been involved in fishing in the Halda for generations. We have seen the river lose many species over the last 10 years. Nowadays, we do not even find enough fish eggs."
To save the fishery, the government has declared a 40km stretch of the Halda as a sanctuary. About 2,000 fishermen along the river have become unemployed as a result. Many have been forced to change their ancestral profession. Some pull rickshaws, while some work as day labourers, he added.
Rare Gangetic dolphins under threat
It is not only the fish that are vanishing in the Halda. The river is also the habitat of the Gangetic dolphin, an endangered species. It is now under extreme threat.
Dr Md Manzoorul said Gangetic dolphins can be found in Halda and Karnaphuli and the Ganges river in India. Once there were 167 dolphins in Halda but now the number is 126. In the last three years since September 2017, 29 dolphins have died in this river."
Following a writ petition, the High Court on 19 May 2020 directed the Chattogram district administration to form a special committee composed of local administration and public representatives to protect the biodiversity of the Halda river, mother carp fishes, and dolphins.
Hathazari Upazila Nirbahi Officer Ruhul Amin, a member of the committee, said the committee has been monitoring the area round-the-clock. It also held several virtual meetings, and conducted drives to stop sand extraction from the river.
However, even after their initiative, the killing of mother fish and illegal extraction of sand in Halda have not stopped. A dead dolphin was recovered from Halda last Tuesday.
In 2007, the government declared the area from the estuary of the river Karnaphuli to Fatikchhari Nazirhat as a sanctuary. In 2018, the government imposed a ban on any kind of sand extraction, movement of mechanical boats and netting. However, there are allegations that these restrictions are not properly enforced. As a result, many dolphins and mother fishes die due to injuries.
Professor Manzoorul Kibria said, "Sand-carrying dredgers would not be able to run on this river if the administration was active. Adjacent factories would also not be able to pollute the river."
Gangetic dolphins are freshwater creatures. The dolphin's habitat is also under a threat owing to salinity. When salinity in the water increases, dolphins, like mother fish, will lose their habitats and move upstream, he said.
Rising sea level
According to the data of the Hydrology Department of the Water Development Board, the water level at Kalurghat point and at the junction of the Halda and the Karnaphuli rivers has crossed the danger level six times in the last eight years. In 2017, the water level increased to a maximum of 4.98 metres.
Wahidul Alam, associate professor of the Department of Oceanography, Chattogram University, told The Business Standard, "Sea level is rising all over the world due to climate change which is the reason behind the increase in salinity in the Halda and the Karnaphuli rivers. Biodiversity of these rivers is also changing."
Chattogram Wasa in crisis
Chattogram Wasa withdraws 180 million litres of water per day from two projects on the Halda river for about two million people in Chattogram city. But due to the increased salinity, they have to stop pumping water from the Halda. Not only that, to make the water suitable for drinking, they need to reduce the level of salinity by extracting and blending groundwater from 37 tube wells.
Currently, the amount of salt in the water supplied by Chattogram Wasa is 350 ppm, which usually stays within 200 ppm. Excessive salt in the Wasa water has led to frequent outbreaks of diarrhoea among city dwellers.
In 2018, the salinity in the Halda river increased so much that the Wasa was compelled to publish a notice in newspapers asking people not to drink the water.
Chattogram Wasa Managing Director AKM Fazlullah said, "Our water contains 200 to 250 ppm of salt. Now, the amount of salt in water has increased to 350 ppm, which is not harmful to health. Although we are against extracting groundwater, most of the time we have to blend groundwater with river water."
Meanwhile, Chattogram Wasa is looking for an alternative source of water to supply water to Bangabandhu Sheikh Mujib Industrial City because of the rising salinity in the Halda river and objections from environmentalists.
"We are now thinking of bringing water from the Meghna River. A concept paper has already been sent to the local government ministry," added Fazlullah.