Kolleru, 15 km from Eluru, is one of the largest freshwater lakes in India — 674 sq km at normal water levels, swelling to over 900 sq km during the monsoon. It sits in a shallow basin between the Krishna and Godavari deltas and acts as a natural overflow for both rivers.
From November to March the lake fills with migratory birds: painted storks, openbill storks, grey herons, white ibises, egrets, teals, pintails and shovellers, plus large numbers of resident waterfowl. Atapaka Bird Sanctuary, on the southern shore, has watchtowers and a small visitor centre and is the easiest place to see them. The lake was designated a Ramsar wetland of international importance in 2002 after years of pressure from conservation groups.