The Hindu : Karnataka / Bangalore News : `Fall in oxygen level led to death of fish'

Online edition of India's National Newspaper
Friday, Jan 28, 2005

Karnataka

Karnataka - Bangalore

`Fall in oxygen level led to death of fish'

By Our Staff Reporter

Bangalore Mahanagara Palike workers removing dead fish from the Ulsoor Lake in Bangalore on Thursday. — Photo: V. Sreenivasa Murthy

BANGALORE, JAN. 27. Even as more fish were killed on Wednesday night in the Ulsoor lake leading to a foul smell around it, the Karnataka State Pollution Control Board has found that decreased level of dissolved oxygen in the lake has led to their death.

K. Saibaba, Member-Secretary of the Board, told The Hindu that the level ranged from one milligram per litre (MPL) of water to 1.9 MPL in samples collected from different parts of the lake.

Fish population

Preliminary observations indicated that the large fish population in the lake could be a reason for the decrease in the oxygen level. He said more fish could have been let into it than it could take. The Gambuzia variety particularly, which has been let into the water for controlling malaria (as it feeds on mosquito larvae), is a fast breeder.

He ruled out toxic elements causing the death. "There is no toxicity," he said.

Several other parameters and presence of chemicals such as nitrates and phosphates are being analysed. A final report will be ready in two days, he said.

It is not yet known what exactly reduced the level of dissolved oxygen in the lake.

The possibility of sewage water polluting the lake is being looked into. The drainage lines leading to the lake have been diverted as part of the restoration and beautification of the lake, he said. The Biological Oxygen Demand (BOD) that indicated the total amount of oxygen required to maintain the purity of the lake water, is also being analysed, he said.

Board sources explained that a lake will require more oxygen to purify "organic load" (drainage water), the presence of which can cause an increase in the BOD level. If the BOD level is more than the available oxygen level, it will mean that the lake is polluted.

Steps suggested

The Board has suggested measures to increase the oxygen level, such as installing floating aerators, which rotate and supply more oxygen from the air into the water, and releasing potassium permanganate into the lake to purify it.

Bangalore Mahanagara Palike (BMP) sources said that the suggestions would be considered. They said the investigation reports on the fish kill were awaited.

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