Fish kill: sewage and pollutants are the main culprits

KSPCB has been inspecting water bodies after the fish kill in Ulsoor lake on May 9

Early this month, residents around Ulsoor lake woke up to the unbearable stench of thousands of rotting fish. It was not the first time that the lake had become a burial ground for its aquatic life. But what was unusual and cause for worry was that it was the second fish kill in a short span. In March, more than a lakh fish were found dead, floating in its calm waters.

The news made national headlines, but officials say that fish kill is not unique to Ulsoor lake ( see box ).

“Following the latest incident at Ulsoor, we visited 25 lakes since May 9 and found a pattern,” said Lakshman, Chairman, Karnataka State Pollution Control Board. Many of the storm-water drains, which lead to the city’s water bodies, have either disappeared or turned into sewage drains. “They have not been cleaned for a long time, and polluted water is dumped in lakes. Besides this, garbage is dumped in the lake. Also, construction debris,” said Mr. Lakshman. Lakes in Devarabisanahalli, Karihobanahalli and Agara were among those that the KSPCB inspected.

“What is needed is regular clean-up of storm-water drains to ensure that they are in working condition. If special attention is paid in the monsoon, it is even better,” said Mr. Lakshman, adding that the pollution board is in the process of making a detailed report on how fish kill can be avoided.

Over breeding

KSPCB has cited overcrowding as one of the reasons for fish kill. “In most cases, breeders put 30,000 fish in a lake meant to accommodate only 10,000. These fish breed more fish and, in the end, there are too many of them, fighting for oxygen and food leading to their death,” Mr. Lakshman said.

The KSPCB’s views are echoed by Kavitha Reddy from Agara Lake Protection and Management Committee. “Varieties of fish for ornamental purposes are being bred here for whom the temperature conditions are not suitable. This could also be a reason for the fish kill,” she said, adding that despite all the hue and cry and promises by the authorities, no steps were being taken to solve the problem.

“I have been studying lakes in the city since the 1990s. The situation is serious,” says IISc. Prof. T.V. Ramachandra, who led a study titled ‘Recurring fish mortality episodes in Bangalore lakes’. He says that the causes for large-scale fish kill are similar.

While a major portion of the dumped solid waste is bio-degradable, the nutrients seep into the water after they are broken down, which coupled with sewage, lead to an increase in concentration of ammonia and other nutrients in the water, says the report.

The Bengaluru District Fish Production, Processing and Marketing Cooperative Society, which breeds fish at Ulsoor and other lakes, released a statement saying: “There was a big rain on May 6 and the storm-water drains were flooded since they had not been cleaned. These drains were stuffed with plastic and other waste, which gushed out into the lake. This resulted in decreased dissolved oxygen (DO) level, leaving the fish fighting for oxygen.”

Rs. 4 crore for STP in Ulsoor lake

The KSPCB said Rs. 4 crore will be allotted for construction of a sewage treatment plant in Ulsoor lake. KPSCB Chairman Lakshman said the BWSSB has been directed to get the plant working within a year. The KSPCB has issue a notice to the BBMP following the fish kill, he added.

Solutions Allow only treated sewage into the lake

Pass treated sewage through constructed wetlands (to remove nutrients). This model has been working satisfactorily at Jakkur lake

Improve aeration (to enhance dissolved oxygen levels) through water fountains

Ban plastic in the vicinity

Penalise polluters

Remove all encroachments on drains leading to the lake

Route the drain to integrated treatment plant (STP with constructed wetlands)

Ban introduction of exotic fish species

(Sourced from the IISc. study — Recurring fish mortality episodes in Bangalore lakes)