According to Indian Institute of Science (IISc), the fish mortality cases in India have grasped headlines and often found written in research papers, the maximum are from Bengaluru followed by Mysuru, a recent study has revealed.
Most fish have perished for the same reason. Continuous flow of untreated sewage and chemicals into water bodies has caused dissolved oxygen (DO) levels to dip, the study on Frequent Fish Mortality Occurrences in Bengaluru Lakes by Indian Institute of Science (IISc) has found. If not then, the authorities must now take legal action against clearing the dead fishes from the water bodies.
"Ulsoor Lake falls under category E of Inland Surface Water, which means the water can be used only for irrigation, industrial cooling or controlled waste disposal," said professor TV Ramachandra of the Centre for Ecological Sciences, IISc. He added, "The sustained inflow of untreated sewage into the Ulsoor Lake has flooded the aquatic ecosystem with nutrients." Algae (also harmful to aquatic life) grow well under high nutrient availability.
11 years back then the first incident took place where Ulsoor Lake witnessed its first fish kill 11 years ago in January. Increased oxygen demand and chemicals flushed into the lake were to the actual cause. The second incident happened in January 2005 when pollutants flowed into the lake after the Ulsoor swimming pool was cleaned. The third such incident was recorded on March 7 this year where oxygen levels dropped to dreadfully low levels (zero at some points) due to entry of untreated sewage.
The analysis of water samples and fish samples by IISc researchers reveals the fish mortality in Ulsoor and Devarabeesanahalli lakes was due to asphyxiation, with a sudden and considerable fall in DO levels in some locations.
According to the reports, Besides Bengaluru, two lakes in Mysuru, (Kukkarahalli and Karanji) witnessed incidents of fish mortality in 2001 and 2014 respectively lake due to discharge of effluents. Even Taj Boudi in Bijapur witnessed the frequent occurrence in 2010. Andhra Pradesh fares the second worst with over five occurrences of fish death in over a decade. AP is followed by Madhya Pradesh and Kerala
To avoid such situation further IISc has recommended few necessary steps:
*Aerators (water fountains) or introduction of ducks. Aeration will increase DO levels and minimize hydrogen sulphide, methane and various volatile organic compounds responsible for bad taste and odour
* Regular monitoring of lakes will help understand physico-chemical characteristics
* Dredging (mostly wet dredging) will remove sediments (rich in nutrients)
* Public awareness and participation necessary to safeguard lakes
The condition of Ulsoor has worsened and Until Tuesday, the corners of Ulsoor Lake were infested with garbage and dead fish. According to the TOI reports, little had changed except that the trash and fish were strewn all over the lake's surface. The area was isolated and no work was going on.
Babu was present at the spot, refused to reveal which department he's from. He informed that the strong wind had caused the fish to strew. "We have started the clean up on Wednesday; it's expected to be over in a week. We have divided the work among eight people — while the fishermen are collecting the dead fish, the others are picking up the garbage" he said. "The waste is being offloaded at a spot in Kannur. But if it rains, it will take us two more weeks to clean the area," added Babu.