Shoals of fish have been found dead and floating on the Sumendu Lake, a prominent tourist spot located in the heart of hill town Mirik in Darjeeling district, over the past 48 hours.

The incident has left the residents and conservationists worried.

A sudden rise in pollution levels of the lake might have caused the fish deaths, they have said.

“Since Sunday, over 200 fish have been found dead and floating on the lake. We have informed the departments concerned, including the fisheries, the local civic body and the Gorkhaland Territorial Administration (GTA),” said A.T. Rai, an employee of the tourism department of the GTA posted in Mirik, on Monday.

Located around 55 kilometres from Siliguri, Mirik is known for the scenic lake made in the early seventies.

The 1.25km-long water body is a major tourist spot in the Darjeeling hills and provides a livelihood for many residents of the tiny hill town.

Officials of the state fisheries department mentioned that some research suggests that human-made pollution is one of the major reasons for the rise in pollution levels of the lake’s water.

On May last year, a similar incident occurred when dead fish were found floating in the lake, they pointed out.

“We have been carrying out regular cleanliness drives across the embankment of the lake area. But the sewage from many spots in the town is still discharged into the lake, which leads to pollution,” said an official.

Animesh Bose, the programme coordinator of Himalayan Nature & Adventure Foundation (Hnaf), a Siliguri-based organisation that has been working on the conservation of nature and biodiversity, said the incident is a threat to the aquatic life of the lake water, an important biodiversity site in the hills.

“It seems polluted water has become a major threat to the aquatic life of the lake. Immediate steps are required to protect the rich biodiversity of the water body,” said Bose.

Sources said that in August last year, the state took up an important project — installation of a sewerage treatment plant (STP) in the Mirik civic area.

The project aimed to connect 1,057 households close to the lake so that polluted water is not discharged into the lake and such water is passed through the STP.

A sum of ₹8.61 crore has been allocated for the project. Work is in progress.

Koushik Maity, the district fisheries officer of Darjeeling, said a meeting was held last week in Siliguri in the presence of Roshni Sen, the additional chief secretary of the state fisheries department, on the health of the lake.

“At the meeting, she had instructed the speedy implementation of the STP to check pollution in the lake,” said Maity.

He said that Cyprinus Carpio (American rohu), trout and silver carp, which can survive in cold water, are found in the lake.

He said that fish are released into the lake throughout the year, but angling is not allowed. “There may be a dip in dissolved oxygen in the lake. We have collected samples. Tests will reveal the reason for fish deaths,” he said.