Nagpur: Although Nagpur Municipal Corporation (NMC) took some steps to ensure eco-friendly immersions, the condition of the city lakes only seems to be degrading as compared to previous years. A scientific survey conducted on Sunday by city-based NGO Green Vigil in three big lakes of the city, Sonegaon, Telangkhedi (Futala) and Gandhi Sagar, revealed that barring Sonegaon, dissolved oxygen levels in other two water bodies have gone down drastically. Raising concern over the deteriorating condition of the lakes, experts warned that further fall in dissolved oxygen level will result in collapse of the entire lake ecology. Green Vigil member Surbhi Jaiswal informed that they collected and analysed water samples at the immersion sites and found that the condition of Sonegaon Lake was not much affected. "We tested the water on three basic parameters, including pH value, turbidity and dissolved oxygen. The level of dissolved oxygen and turbidity was recorded around 5 mg/l and 45-50 JTU respectively pre and post immersion," she said. In the last week of July this year, the NGO had collected and analysed water samples of these lakes to get the pre-immersion values. The situation is worse than last year at Telangkhedi Lake, which witnessed maximum immersion of idols. "Even before the immersions, the level of dissolved oxygen was 3.5 mg/l which is quite low. Last year, it was better as the civic body had conducted a cleaning drive before immersions," said co-founder of Green Vigil Kaustav Chatterjee. The post-immersion value of dissolved oxygen in Telangkhedi lake has reduced to 2-2.5 mg/l and the turbidity of the lake has gone up to 60-70 JTU. At Gandhisagar lake, the pre-immersion value of dissolved oxygen was recorded as 4.5mg/l which has today reduced to 2.5 mg/l. The turbidity of the lake has also increased to 80 JPU. The members also saw some dead fish floating near the banks of Gandhisagar lake. "Turbidity refers to the presence of suspended solids, whose quantity increased post-immersions due to discharge of nirmalya in the water bodies. As city lakes have no other source for artificial oxygen supply, atmospheric diffusion is the only source. When the level of dissolved oxygen gets low, fish come to the surface of water but often die due to high temperature," said Chatterjee. He added that if the level of dissolved oxygen gets below 1.5mg/l, the entire ecosystem of the lake would collapse. "It will be a huge loss of biodiversity and civic authorities must take it seriously," he added.