Sarobar health worry: Depth reduces, shallow zones and silt grow at Kolkata lake
Times of India | 13 July 2025
Kolkata: Rabindra Sarobar, the place where many go for a stroll in the morning or evening is itself not in the pink of health, a recent bathymetric study of the lake that measures a waterbody's depth has revealed. A primary survey report shows that the lake's shallow zone, having depth of less than two metres, increased by 7% between 2022 and 2025.
The report also shows that the lake — spread across 73 acres — has been experiencing an average yearly siltation rate of 8.3 cm since 2022.
The survey was commissioned by Kolkata Metropolitan Development Authority (KMDA), the custodian of Rabindra Sarobar. It was conducted by the School of Water Resources Engineering, Jadavpur University, taking the period between 2022 and 2025 into account. Field data was collected by a team of experts using motorised vessel navigating a GIS-based grid. As per the survey report, there has been a minimal but progressive loss of the lake's depth in the last three years. The mean depth of the lake decreased from 3.2m in 2022 to 3m in 2025. The maximum depth of the lake reduced slightly from 5.1m to 4.9 m. The study found that approximately 35% of the total lake area falls within the deep zone, which has a depth of over four metres. About 37% of the lake area falls within the moderate depth zone of two to four metres and the remaining 28% of the lake area makes up the shallow zone. It is this shallow zone that acts as sediment traps.
The overall quality of the waterbody was found to be more or less satisfactory, and the dissolved oxygen level was also found to be satisfactory. However, there is some metallic sedimentation with high contents of zinc and magnesium in the shallow zone of the lake bed, which may be toxic in nature.
The survey report suggests conducting eco-sensitive dredging with deep water protection measures. A sustainable dredging strategy, prioritizing the silt-laden shallow areas while preserving the ecologically sensitive deeper basins of the lake has been recommended in the study.
"There is a proposal to conduct dredging of the waterbody. The expert committee on Rabindra Sarobar lake preservation has recommended widening the range of the bathymetric survey study from three to 20 years so that a more comprehensive and modified report could be analysed before a decision on dredging could be taken. The ecological impact of the dredging procedure is also to be assessed after the modified bathymetric survey report is received," said a govt official.
"The lake has not undergone proper desilting for two to three decades, leading to reduced water depth. Sustained efforts are necessary to protect the lake's ecosystem and biodiversity," said environmentalist and lake regular, Somendra Mohan Ghosh.