Bengaluru: Mass fish deaths in Bengaluru’s lakes are the consequence of extreme mismanagement of the city’s fragile and ecologically vital lakes and wetlands, a study by the Indian Institute of Science (IISc) said.
IISc started the study after mass fish deaths in Ulsoor lake two months ago, the latest in a series of events revealing the state of pollution in Bengaluru. Foam covers the surface of Bellandur, the city’s largest lake, which caught fire twice last year.
After studying samples of water and dead fish from Ulsoor lake—a major source of drinking water for Army troops in the early 19th century—IISc said the fish choked to death after oxygen levels in the water suddenly fell sharply.
Steady flow of untreated sewage into the lake and high levels of certain toxic substances could have depleted oxygen levels, the study said. “The physico-chemical characteristics of Ulsoor lake reveals depletion of oxygen, high turbidity and organic contents, high biochemical oxygen demand (BOD) and ammonia toxicity," noted the research report.
“Fish usually require a minimum of 5 mg/L (milligrams per liter) of dissolved oxygen (DO). They can tolerate below 2 mg/L for short periods, but they will start dying when the DO drops below 1 mg/l," said T. V. Ramachandra of IISc’s Centre for Ecological Sciences, who supervised the study. “The summer heat could have enhanced the effect but Ulsoor is an indicator of environmental stress, declining of aquatic ecosystems health and water quality problems," he said.
Ramachandra said when the research group was gathering newspaper reports on recent mass fish deaths in India as part of the study, it found most of the fish deaths were reported in Bengaluru.
Recurring episodes of fish mortality, algal bloom, profuse growth of invasive exotic weeds, introduction and rearing of exotic species highlight administrative mismanagement, said the study. Despite significant service to the local geography, wetlands are being encroached, polluted and constantly abused by senseless and irresponsible urban decision makers, it noted.
The study, which was published on 30 April in ResearchGate, a social networking site for scientists and researchers to share papers, says eight simple measures could help revive Ulsoor lake. They include regular monitoring of water quality, measures to maintain healthy, dissolved oxygen levels using aeration, allowing only treated sewage into the waters and slapping a penalty on polluters to finance revival schemes.
Will the study be a wake-up call for the administration? Environment activist Zaffar Sait does not think so. Sait said he had presented a documented survey of Ulsoor lake to chief minister Siddaramaiah last July, but is yet to receive a response. His photographs show sewage, plastic, thermocol, clothes, blood from slaughterhouses and fecal matter mixing with water that goes into Ulsoor lake from various locations.
Fish deaths were reported from Ulsoor lake this week as well. Garbage could be seen floating over the lake’s waters, despite the state government’s assurance to remove trash from waters after the March incident. A call to environment minister Ramanath Rai went unanswered.