Bangalore: Bangalore's biggest lake, which receives more than 40 per cent of the city's sewage, was up in flames for over a day till 800 soldiers and 100 fire-fighters succeeded in dousing the fire on Saturday afternoon.

Some 400 litres of waste is flushed into the 3.6sqkm lake in the southeastern suburb of Bellandur every day, covering it in a two-foot-thick oily layer, former state pollution board chief Vaman Acharya said.

He said the lake, covered in froth during the rains, has been catching fire every winter "for the past 21 years" but this year's blaze was the biggest.

"Local villagers light fires on the lake's grassy banks to warm themselves, and the cowherds who graze their cattle there often smoke. It's difficult to say what caused the fire," Acharya said.

Lakshman, the current pollution board chairman, did not answer calls.

Officials said the blaze destroyed large tracts of grasslands on the banks and killed at least one cow. The residents of the blocks of flats around the lake had to endure thick fumes since Friday afternoon.

The minister for Bangalore development, K.J. George, ordered a police investigation to rule out foul play. "We are committed to rejuvenating the lake and have taken several initiatives," he said.

However, since the National Green Tribunal took suo motu cognisance and asked the state government last February to tackle the problem, the authorities have merely weeded a portion of the lake and prepared an expert committee report on its rejuvenation.

Officials said the sewers in densely populated Bellandur were not connected to the city's main underground network that carries sewage to a treatment plant. They admitted that some of Bangalore's other 85 lakes too received some sewage locally, but in smaller amounts.

Acharya, now a BJP spokesperson, said he would not blame the Congress government for the situation in Bellandur.

"The larger question is, who gave permission for houses and apartments to come up in such a vast area without connecting its sewers to the underground sewerage network," he said. "Even during my tenure we kept telling the government to take matters seriously."

Although the lake is a stone's throw from an Army Service Corps Centre that is home to 5,000 personnel, this was the first blaze that required the soldiers to be deployed.

"It's never been like this, so we sent about 800 of our men," Lt Gen. Vipin Gupta, commandant of the centre, said.

Sridhar Pabisetty, CEO of the Namma Bengaluru Foundation, a citizen's forum that became a party to the NGT case last year, said the problem was a blot on the city.

"Stop flushing sewage into the lake, and much of the problem gets solved. Then it just takes some determination to clean up the lake," he said.