Geospatial Analysis of the Changing Environment of Kolleru Lake, the Largest Freshwater Wetland in India

Kolleru Lake, the largest freshwater wetland in India is highly degraded because of siltation, weed infestation and large-scale aquaculture encroachments. Restoration of the lake involves data on the original extent of this shrinking lake and on its extant condition. Previous studies indicated that the lake was a coastal lagoon abutting the Bay of Bengal during the mid-Holocene and later turned into a freshwater body as the seashore prograded 30 km and several rivulets continued to drain into the lake. However, the original extent of the lake is unknown. Mapping of geomorphic features from satellite images and facies recognition from the subsurface sediments recovered from 40 boreholes revealed that the lake initially extended over 1050 km². Analysis of time series satellite images indicated that aquaculture activity was absent in 1977 in the 493 km² designated Kolleru Wildlife Sanctuary within the 5 ft (~1.5 m) contour but appeared in 12 % of the area in 1990 and expanded to 64 % by 2004. Despite the demolition of fishponds by the government during 2005–2006, they reappeared in 28 % of the sanctuary area by 2008 and further increased to 43 % by 2015, as encroachments continued unabated.