The floods caused by Nilam in the various drains that empty into Kolleru Lake have caused the water to rise up and cross the +8 contour. The Kolleru Lake is a Ramsar Site and the water body and islands within +5 contour have been declared a Wildlife Sanctuary and are protected under the Wildlife Protection Act.
While several drains empty into the lake, a depression between the deltas of Krishna and Godavari Rivers, the Budameru drain that is in spate is the main cause for the increase of water level in the lake.
According to the P.A.Azeez report, the lake covers about 901 square km within +10 feet contour, 673 square km within +7 feet contour, and 135 square km within +3 feet contour. In monsoon, the lake spreads generally over +5 feet contour with a water holding of 300 million cubic metres.
Every few years, the lake spreads over +7 feet contour and the storage of water at this level would be 508.4 million cubic metres. On an average once in eight years the lake fills to above +9 feet contour, holding up to 1222 million cubic meters of water in contrast to the storage of about 150 million cubic metres at near about +3 feet contour.
If the lake is resized by reducing its effective functional area, inflow during rains would spread far wider and away into upstream areas submerging bed and belt villages, and at times the towns of Eluru, Gudivada and Vijayawada, the report said.
The report also gave details of the number of villages that get submerged when the lake swells in size. If water in the lake crosses the +5 contour 22 villages in Krishna and 38 villages in West Godavari get marooned, if it touches +7 contour ten more villages in West Godavari get marooned and if the water rises to +10 contour and another 23 villages in West Godavari get marooned.