Hundreds of fish floated dead on the Teesta river near Jalpaiguri town on Tuesday, raising concerns that anti-social elements had poisoned the water.

Residents of South Sukantanagar noticed the dead fish while heading to the riverbank with their cattle on Tuesday morning. They claimed that nearly 10 varieties of fish were found floating lifeless in the water.

Many residents suspect that the deaths were caused by deliberate poisoning of the river.

“We go to the riverbed daily with cattle. We saw many fish floating on the water this morning. Some people even collected the dead fish. We don’t know what caused the deaths,” said Gobinda Chanda.

Ramesh Chandra Biswas, the assistant director of the district fisheries department, said over the phone: “I am currently in Calcutta on election duty. Instructions have been given to collect samples of water and dead fish for tests.”

Members of the environmental volunteer group Prakriti Premi Jalpaiguri visited the site.

Dipanjan Bakshi, the organisation’s secretary, said some local people had already taken away the dead fish.

“From what we observed, around 10 species of fish have died. It appears similar to the earlier Karala river incident. There is a possibility that pesticides or poison have again been mixed with the water,” he said.

In February, a large-scale fish death was reported along a stretch of nearly 1.5km of the Karala, which flows through Jalpaiguri town.

Residents said several species, including large catfish, snakehead, rohu, katla, ritha and bata, were found dead in the Karala. Apart from residents, many fish vendors were also seen collecting the fish from the Karala.

At that time, preliminary investigations by the fisheries department indicated that pesticide contamination in the river water caused the deaths of around 15 species of fish.

“We are, however, yet to get the laboratory reports of the samples sent to Calcutta after the February incident,” said an official of the department.