Thousands of dead fish surface at Bengaluru's Ulsoor Lake

Residents living in and around the lake found the dead fish floating on the surface, raising an unbearable stench.

A similar incident happened on March 7 involving thousands of dead fish. The lake and pollution authorities made a lot of noise about this.

"This place was once such an ideal place to live, with fresh water and greenery all around. Everything's stinking now literally," said Ashok, a resident of the upmarket area in Ulsoor.

Authorities collected nearly 200 kg of dead fish but evening joggers said there were plenty more still lying around.

"Due to pre-monsoon showers, sewage entered the lake through storm water drains...as did a lot of garbage? that has been the primary reason," one of the officials said.

According the Karnataka State Pollution Control Board, dissolved oxygen levels are to be blamed. The DO levels on Tuesday were below 1mg/litre, and the limit set by the Central Pollution Control Board (CPCB) is 4mg/litre.

After the last episode of fish kill, the Bengaluru Mahanagara Palike (BBMP), which is in charge of this lake, was asked to arrest sewage flow and install aerators. Though BBMP claims to have done it, locals say that the work is incomplete.

One look at the dead fish, and you know the open mouths point out to oxygen deficiency. "So you know the grills and the treatment plant here are not doing the job and the authorities are not monitoring it. Clearly, lessons not learnt," says Shanti Ramakrishnan, a long-time Ulsoor resident.

A tourism spot, Ulsoor lake had been choked with water hyacinth in recent years, with government launching clean-up efforts.