Fish in Hakaluki Haor have started dying since Sunday as half-ripe paddy submerged under flashfloods continues to rot and pollute its water.
It is a double blow to the livelihoods of people dependent on the waterbody after the flashfloods damaged hundreds of acres of Boro paddy just weeks ahead of harvest.
Rotting fish are spreading an unbearable stench and posing health hazards.
"I lost my Boro crop. I thought we could survive with the fish in the haor. But now, all the fish are dying,” said Rahim Uddin, a fisherman from Bhuksimul union in Moulvibazar's Kulaura upazila.
People in the haor areas under Sylhet division are going through a similar situation due to the flashfloods late March caused by incessant rain and the onrush of water from upstream.
Different species of fish -- puti, tengra, bheda, baila, pabda and ruhi -- are dying in Hakaluki Haor, one of the country's largest haors, and have started rotting, said Sultan Mahmud, senior fisheries officer of Kulaura.
Acidity in the haor water has also risen. A pH level of 7.5 to 8.5 indicates normality but now it is 5.8, Sultan told The Daily Star.
Insecticides used in the crops have also dissolved in the water, causing fish to die, he said.
The local administration has urged people to refrain from consuming the fish.
Yesterday, this correspondent found different aquatic plants rotting in the haor.
Sona Miah of Bhuksimul village said dead fish, especially big varieties like ruhi, katla, mrigel, kalibous and grass carp, were found floating in the water.
He said birds living in and around the waterbody were becoming sick as they were eating dead fish.
Saytakan Chakraborty, civil surgeon of Moulvibazar, said the water might cause different diseases and called upon locals to be cautious in using it.
Tofazzal Sohel, general secretary of Bangladesh Poribesh Andolon of Habiganj unit, told this correspondent that he saw a lot of dead fish floating in the water while travelling through a waterbody in Ikram area under Baniachang upazila of Habiganj.
Wahidul Abrar, fisheries officer of Sunamganj's Jagannathpur, said ammonia gas was created in haor water from the rotten paddy. Fishes were dying due to the gas.