With the rising pollution and increased human activity, the natural ecosystem of Powai Lake seems to have gone for a toss, killing many fishes earlier this week. Alarmed by fish corpses floating on the lake surfaces, Maharashtra State Angling Association (MSAA ) has informed BMC about it after conducting a field investigation of the lake between March 24 to March 26.
The maximum number of fishes that were found dead were Rohu and Mrigal, then Catla and Tilapia.
"As a group of environmentalists protecting the fish and fauna and precincts of Powai lake, we patrol the lake 24 hours. On March 24 2021 at 7.30 am our watch and ward staff observed large specimens of fishes showing signs of extreme distress and swimming on the surface of the lake. After having closer look at it, several fishes were found to be dead," said Kamlesh Sharma, secretary of the Maharashtra State Anglers Association (MSAA) adding that they immediately initiated a field investigation.
"This is an indicator of ecological imbalance and environmental degradation. The exact cause is a mix of multiple factors acting simultaneously and spontaneously," added Sharma.
According to the field investigation report of MSAA, the factors of the dying fish is the fluctuation of Dissolved Oxygen (DO) level (Low oxygen level at early morning time), Clogging due to Blue-green algae in the gills of the more vulnerable species of fish.
"Most dominant species of Blue-green algae which is lethal to fish and fauna are Microsystis, Merismopedia, and Anabaena sp. The sudden bloom is caused by nutrient enrichment and bright sunlight. Bright sunlight is natural at this time of the year. However the nutrients are mainly due to domestic waste which is being discharged from Northside and towards Ganesh ghat side of the lake," the report stated.
The water quality of Powai lake has highly deteriorated. The colour is greenish caused by the abundant bloom of Blue-green algae. There was a very bad fishy smell emitting from water, the report further stated.
Dr. Pramod Salaskar, Secretary of Naushad Ali Sarovar Samvardhini (NASS), who has been studying the Powai lake ecosystem for several years now and has conducted water tests too, said that the biggest reason behind the low transparency is the increased growth of blue-green algae, which has also rendered the colour of the lake green. "The problem started aggravating in the last decade. The water level is decreasing every year after the monsoon due to the rapidly changing climate and the rising temperature. The amount of green algae has declined and the amount of blue-green algae has increased which is lethal for the fauna in the lake," Salaskar said.
He added," I have been following this for a year now. The amount of oxygen in the water is an important indicator of overall lake health. DO is the most important parameter which can be used as an index of water quality and pollution. With the drop in DO levels, it is clear that the pollution level at Powai is increasing at an alarming rate. Large fluctuations in DO levels over a short period of time may be the result of an algae bloom, and this is deadly for a water body.”
Dissolved oxygen is an important measure of water quality, as it is a direct indicator of a water body’s ability to support life. Powai Lake is home to carp, eels, and other varieties of fish, apart from a small colony of crocodiles, but has already lost many native species.
According to MSAA, the remedy to prevent Powai lake from dying is to immediately stop all inlets through which sewage enters the lake. They have stated that the BMC was aerating the waters by a network of technically designed water aeration systems installed over the last months. The current arrangement of the aerator is not effective at Powai Lake, they concluded.