For some residents near the Ulsoor Lake, there was no respite on Saturday from the stench that had been prevailing in their neighbourhood.

A part of the lake, near the RBANMS First Grade Evening College, was covered with a thick, slick, blue-and-green film and water had left a green-coloured layer on the tank walls. Plastic bottles and other articles were seen floating on the film.

However, manual cleaning of the lake was being done by three men on Saturday. The stink from the lake is due to the stealthy immersion of Ganesha idols in the lake, said Venkatesh Murthy, in-charge of the lake and Assistant Engineer, Bharatinagar Division, BBMP. The chemicals, paints and dyes from the idols have left the colour and stench, he added.

However, the contractor of the idol-immersion and cleaning of the tank, Vishwanath said, that the reason for the formation of the film could be the leakage of oil from the motor boats of Madras Sappers.

Mr Vishwanath  also stated that the film was spread in an arch of around 100-metre radius from the corner of the lake near the RBANMS College.

“Now, after cleaning for three days, the area has reduced to an arch of 10-metre radius,” said Suresh of BBMP, who has been overseeing the cleaning work. The filth is concentrated only in a part of the lake at a corner due to the direction of the wind,  Mr Suresh added.

BBMP has written to the Karnataka State Pollution Control Board but the sample of water can be taken for test only on Monday as Saturday and Sunday are holidays, Mr Venkatesh Murthy said. The lake water will be treated as per the test results, he added.

“Madras Engineering Group (MEG) assisted us yesterday, with a fast-moving machine boat to disturb the water to help in sedimentation. Two machine boats will be used for sedimentation today,” said Murthy and added that the problem had to be dealt with before fishes in the lake started dying.