Rich in flora and fauna, it attracts migratory birds from northern Asia and Eastern Europe between the months of October and March. During this season, the lake is visited by an estimated two million birds. The resident birds include grey pelicans, Asian open-bill ("Anastomus oscitans"), painted storks ("Mycteria leucocephala"), glossy ibises and white ibises. The migratory birds include red-crested pochards, black-winged stilts, pied avocets, common redshanks, Eurasian wigeons, gadwalls, great cormorants, garganeys, purple herons, greater flamingos, green-winged teals, northern pintails and northern shovelers. Kolleru lake contains numerous fertile islets called lanka's, many of the small ones are submerged during floods. The origin of unusual depression which forms the bed of the lake is unknown, but it was possibly the results of an earthquake. Therefore, many ancient villages are precepted in the bed of the lake as a result of floods and earthquake. Two copper plates of the early Pallava dynasty have been found in the lake, tracing its history to Langula Narasimha Deva (Langulya Gajapathi Raju) a Ganga Vanshi Odisha king, (Oddiya/Odia raju)Vaddiya Rajulu/Vaddi. According to legend, the Gajapathi fort was located at Kolleti Kota on one of the eastern islands of the lake. The enemy general "muhammadan" probably a Bahamany general encamped at "Chiguru kota" located on the shores. In some ways, the lake protected the Odia forces. The enemy finally tried to excavate a channel, the modern-day Upputeru, so that the water of the lake would empty into the sea and the level would fall so that they could attack the Gajapathi fort. The royal Odia army general sacrificed his own daughter to propitiate Gods and ensure his success against Muhammadan and her name was "Perantala Kanama". Therefore, the channel was called Perantala Kanama. Sri Peddinti Ammavari Temple is one of the oldest and famous temples found in Kolleru. The Suryavanshi Gajapatis of Odisha, on the height of their power in the 15th century, ruled over a kingdom extending from the Ganges river in the north to the Kaveri in the south under Gajapati Kapilendra Deva.