Huge quantities of different varieties of fish and aquatic animals were poisoned to death due to the toxins in the Madhabkunda waterfall in the Barlekha upazila of Moulvibazar.
Starting from Sunday, different varieties of fish, crab, amphibians, and aquatic animals living in the stream were affected by the toxic water flowing downstream of the waterfall.
The Forest Department and local sources said the whole area is now emitting the stench of dead animals. If the problem persists, the downstream flow of water would affect the Hakaluki Haor as well, posing a risk to a much wider range of wildlife.
While inspecting the quality of the water body on Tuesday, officials from the Department of Fisheries said they found nothing out of the ordinary.
They claimed the local fishermen may have illicitly applied some organic toxins to kill the fish, in order to be able to catch the dead fish floating in the water.
On a field visit, it was seen that the amount of dead aquatic animals found in the water was less than those found over the previous two days, owing to a joint effort of the Forest Department officials and locals.
Jahir Ahmed and Kabir Ahmed, two local businessmen, expressed their concern over the toxic quality of the water as it is being widely consumed by the locals and wildlife.
"The local, unethical fishermen must be responsible for the situation. They may have intended to catch these dead fishes in the Hakaluki Haor, as the stream flows through the water body," Phila Khangla, a member of a local ethnic minority community said.
Sekhar Ranjan, BIT officer of the Forest Department, assured Dhaka Tribune that a proper investigation is currently underway in order to identify the cause of the problem.
Speaking to Dhaka Tribune, Kulaura Fisheries Department's Senior Fisheries Officer Sultan Mahmud said: "We found the quality of the water normal on Tuesday. We also applied aqua-medicines to improve the quality of the water."
"We believe the situation will be better soon," he added.