Angry residents say they have approached the authorities many times, but to no avail.
"This is a mix of detergent, urine and faecal matter. It is as filthy as it gets. And this in an area that is one of the largest revenue generators in the country, the Whitefield Industrial Area," says Elan Kulandaivelu, an entrepreneur who lives near the lake.
Tausif, a student at the KK High School, about one kilometre away from the lake told NDTV, "We have tested this water. We took samples from bore wells and the Varathur lake, to IISC where T.V Ramachandra is a professor. We have checked it for alkalinity and hardness and know that the lake water is hard and the toxicity is more."
At the Indian Institute of Science, Professor TV Ramachandra, who has been studying the Varthur Lake since 1997, confirmed that the pollution has been getting worse year by year.
"Untreated sewage is entering the water...one part, the nitrates are carcinogenic, the other, phosphates are causing the froth and shows how we are misusing this non-renewable resource," he said.
But Dr Vaman Acharya, chairperson of the state's Pollution Control said the froth is not cause for worry. It's only really about bad smell, he said.
Dr Acharya said it will take the authorities at least a year to clean the lake if they begin now. Meanwhile, the administration plans to set up more sewage plants across the city.