The froth, analysis showed, contained detergent, urine and faecal matter.

Highlights Huge amounts of froth appeared on 3 lakes in April 2015

Tests showed the froth contained detergent and sewage

Little has changed over a year froth last seen in July

Last year in April, Bengaluru's residents got a shock. Three of India's Silicon city's lakes - Varthur, Bellandur and Yemalur - had gone white with foam. Mountains of froth, blown by the wind, were landing on the road, enveloping cars and pedestrians.The froth, analysis showed, contained detergent, urine and faecal matter - the result, experts said, of untreated sewage being dumped into the lakes.A year down the line, the problem persists. The froth made an appearance even in July, when the city was flooded after heavy rains. But while it is yet to ring alarm bells in the offices of the authorities in Congress-ruled Karnataka, the city's children have decided to act on a priority basis.Over 1,000 students of KK School in Varthur, located barely a kilometer from the lake, have written asking Prime Minister Narendra Modi, requesting him to intervene and save the lakes. The postcards - written by students from Class I to 10 -- were posted on Thursday.After the foam made its appearance at the lake, the students of the school had got the water tested at the Indian Institute of Science. A student had told NDTV that the water was found to be hard and its toxicity more than usual.Professor TV Ramachandran of the institute, who had been studying the lake for years, had said some of the pollutants were carcinogenic.But the city's environmental authorities had brushed away the health aspect, claiming only the smell was some cause for worry. At the time, they also said if work was started immediately, it would take a year to clean the lakes.