After a large number of dead fishes were seen floating on the surface of Rachenahalli and Jakkur lakes in north Bengaluru in the last one week, experts blamed the inflow of sewage water into the water bodies. This comes after a similar incident was reported in October at Muthanallur lake in Anekal.
Environmental scientist Dr Shobha Ananda Reddy told The Indian Express that the reason behind the deaths of aquatic animals could be the inflow of sewage mixed rainwater into the lakes or the disposal of waste by tankers directly into the storm water drains or the lakes.
“In Bengaluru, the wastewater collection and conveyance network and the manholes are laid inside the storm water drains. During heavy rainfalls, the manholes open up due to pressure and large volumes of wastewater mixes with rainwater and flows into the lakes. It is very important to separate the wastewater network and storm water drains to prevent the water from getting mixed as it leads to reduced oxygen levels in the water. Wastewater leads to higher Biological Oxygen Demand in water as the dissolved oxygen available in the lake water is consumed by the microbes in the sewage. Lack of dissolved oxygen in water results in fishes gasping for oxygen from the air and subsequently, leads to their death,” she explained.
Dr Annapurna Kamath, a member of Jalaposhan, a citizens’ movement for the protection of Jakkur Lake, said due to the heavy rains last month, the storm water drains flowing into the lake carried sewage into the water body, resulting in the death of fishes.
In the past three years, lakes, including Madiwala and Kalkere, have witnessed similar incidents and the experts had pointed at the entry of sewage into the lakes as the major reason.