The Tansa lake, a key source of potable water for the metropolis, started overflowing on Thursday afternoon due to heavy rains in the last couple of days, the Brihanmumbai Municipal Corporation (BMC) said.

Tansa, located in adjoining Thane district, is the second water body after the Tulsi lake to get filled to the brim. "The Tansa lake started overflowing today at 2.50 pm. Last year, this lake had overflowed on July 17 at 6.15 am," a senior civic body official said.