In an alarming trend, a total of eight instances of fish kill were reported in Bengaluru lakes within seven months of 2022, surpassing the annual fish kill numbers in the last five years.
A report, ‘Fishkill in Lakes of Bengaluru (2017-2022)’, released by ActionAid, shows that while six incidents were reported in 2017 and 2018, the numbers came down during the lockdown years between 2019 and 2021.
In the last five years, a total of 32 cases of fish kill were identified in the city. This report is a secondary research, taking news reports as the database.
The report has also identified four vulnerable lakes which are prone to fish kill, based on the number of times of incidence. The Haralur lake, in particular, has seen three cases within five years. The Madiwala, the Bellandur, and the Kommaghatta lakes have had two incidents each.
“Three cases of fish kill in Haralur lake within five years is a matter of serious concern and sewage seems to be the major reason, apart from industrial chemicals, for the fish kill,” the report says.
Entry of sewage seems to be the most common factor in most of these incidents; it has been identified as the main reason for 51% of the cases of fish kill in lakes. This is followed by toxins and chemicals which accounted for 23%. Apart from them, industrial effluents, pesticides and fertilisers and sewage treatment plants (STP) are the other identified causes.
The report further explains, “Sewage constituting 51% seems to be the biggest challenge making lakes vulnerable to fish kill in Bengaluru. Organic matter in sewage uses up the dissolved oxygen (DO) in the lake causing levels of DO to reduce, which ultimately causes fish kill”.
Silt to blame: BBMP
Bruhat Bengaluru Mahanagara Palike (BBMP) officials, however, say that sewage was not the reason. “Fish kill happens when it rains and silt flows into lakes through drains and these silt particles get accumulated in the gills of the fish. This causes oxygen deprivation in them and that is why they die. This is why many cases of fish kill happen around the rainy season. This year, as the amount of rainfall was more, it might have caused a greater number of incidents,” said Ravi K.V., Executive Engineer, Lakes, BBMP.
It can be observed in the report that except for August, cases of fish kill have been reported in all months in the last five years. Most of these incidents happened in May and December (seven and five respectively).
The matter of concern is that despite receiving a good amount of rainfall this year, there are these many cases of fish kill.
“Rainwater generally dilutes the water in the lake. It is worrying that these many incidents have occurred amidst the rainfall, as it must mean that the pollution levels in the lakes have reached severe levels. Entry of sewage is also problematic as it causes anoxic conditions in the water leading to the death of fish (oxygen deprivation),“ said T.V. Ramachandra, Coordinator, Energy and Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science.
The report claims that several fish kill incidents in Bommanahalli region went unnoticed by the Karnataka State Pollution Control Board (KSPCB), as an RTI reply received from the board showed that no incidents of fish kill happened in their limits (in the region) between 2017 – 2022. A total of seven cases of fish kill were recorded in the study during the period in the same region. KSPCB officials were not available for a comment on the matter.
ActionAid has submitted the report, along with some recommendations, to the KSPCB, the BBMP, the Chief Minister, and the Principal Secretary-Environment and Ecology and Additional Chief Secretary- Urban Development.
The recommendations include regular monitoring of the lakes in urban spaces, taking action against lake polluters, testing water quality in lakes, and avoiding the entry of sewage into the waterbodies.
