Ulsoor Lake became a graveyard on Monday morning. Thousands of fish were found dead, floating on the lake’s waters, all victims of the early summer heat and soaring temperature. As the day progressed, they were washed onto the lake’s shore.
By evening, the smell of rotting fish pervaded the air as the civic body had not yet cleared the lake. BBMP officials said that it will be cleared completely on Tuesday, and attributed the delay to Monday being a public holiday.
Fish kill in the city’s lakes have almost become an annual phenomenon, during the onset of summer. “It is usually a direct result of reduced dissolved oxygen level in the water. While algae in the lake release oxygen into the water during daytime, it uses up dissolved oxygen during night time along with the fish creating a big drop in the dissolved oxygen levels. So most fish kills are observed in early mornings,” said a senior BBMP official.
However, eco-activist Leo Saldanah, said that the practice of letting in raw sewage into the lakes exacerbates the situation. “Raw sewage let into the lake will be thick during summer compared to the rainy season, leading to a higher concentration of nutrients in the lake, which also causes drop in dissolved oxygen levels. Add to this the water temperature of the lake will also shoot up leading to such fish kills,” he argued.
Though Ulsoor Lake in considered to be one of the more well-maintained water bodies in the city, sources said that there are multiple inlets of raw sewage into the lake.
Prakash Javdekar, the Union minister for Environment and Forests, said he's looking into it further. "I have ordered an inquiry and sought a report on the fish kill. The colonies around the lakes release their discharge directly into the lakes, which is very harmful," he said.
What causes fish kill?
Increase in water temperature in summer, algal blooms leads to fall in dissolved oxygen levels
Thick inlet of sewage in summer, which results in a reduction of levels of dissolved oxygen
Decrease in level of dissolved oxygen in water causes hypoxia for fish, leading to fish kill
