Dead fish floating in the waters of Rabindra Sarobar over the past four days have raised a stink over possible contamination of the 70-acre lake from multiple sources. Regular visitors couldn’t recall the last time they had seen so many fish dying at south Calcutta’s most popular spot for a walk, jog or just a breath of fresh air. Metro highlights the mystery of stinking fish flotsam that has triggered a frantic hunt for the cause

When did fish start dying?

Fish deaths were first reported on Monday. Since then, more than 100 fish of varying size and species have been found dead in the waters of Rabindra Sarobar. 

Sources in the Calcutta Improvement Trust (CIT), the custodian of the lake, said workers deployed to remove algae were the first to spot dead fish floating near the bank. 

“The cause of death could range from infection to injuries, although none of the dead fish found over the past few days bore any sign of injury that might have been caused by the oars that rowers use,” an official said.

Water samples from the lake have been sent for tests to ascertain if contamination is the reason for the casualties and, if so, what is the source.

Affected species 

The dead fish include rohu, katla and khoyra and have been found across the 70-acre waterbody. 
“There are smal fish just a couple of inches long and also large ones that could weigh up to 15kg,” said Das. 

What a regular visitor saw

Samantak Das, who teaches at Jadavpur University and has been visiting Rabindra Sarobar for three decades, said he couldn’t recall seeing so many fish dying together in all these years.
“The stink of rotting fish was overpowering when I was taking a walk around the lake on Thursday,” he said. 

What do the experts say?

Scientists from the West Bengal Pollution Control Board and Jadavpur University visited Rabindra Sarobar on Thursday to collect water samples (above). The recommended tests include those to find out water acidity, the presence of ammonia, the availability of dissolved oxygen and the biological load on the lake.

The results of these tests would be known after two to three days. The CIT authorities have requested the scientists to intimate them about any alarming findings immediately so that corrective measures can be taken. 

Possible reasons 

• Fish deaths are common between the end of summer and the start of the monsoon. When the weather is mostly cloudy, as it has been for some days, the drop in solar radiation translates into reduced photosynthesis in aquatic plants. This, in turn, means less oxygen being added to the water. 

• Routine water tests show that the lake’s pollution load has been consistently on the higher side.

What are the remedies?

Potassium permanganate and lime are being sprinkled to disinfect the water and reduce the possibility of more fish dying. “We are employing the conventional method of sprinkling a mixture of potassium permanganate and lime. This acts as a disinfectant and can arrest the fish deaths,” an official said. 

But workers couldn’t sprinkle the mixture on Thursday because of protests by regular visitors, many of whom suspected that wrong chemicals were being used.

Is the lake a waste bin?

Waste is illegally dumped in the lake every day, increasing the chances of contamination manifold. A CIT official said it was becoming increasingly difficult to keep an eye on and restrain visitors who sit on the edge of the walkway and throw paper cups, plastic wrappers and other such waste into the waterbody. 

“The beautification of the lake seems to have become its bane. More the visitors, greater the amount of waste being dumped. This is harming the ecosystem greatly,” the official said.

Reporting by Subhajoy Roy and Jayanta Basu; pictures by Amit Datta