The lake extends in a east-west direction to the south of the Sea of Marmara and is located at the western tip of extensive fault area containig Lake Ulubat in the east. The lake, formerly known as Lake Manyas, extends in a east-west direction. Twenty 20 km. long and 14 km. wide, it is a eutrophic freshwater lake The level of the lake, which is generally shallow, rises in spring, falling again at the end of summer and in fall when it drops as low as 1.5 m. Its deepest point, at high water level, is 10 m.and its average depth 4 m. The lake is fed by the Kocacay (Madra Stream), which forms a long delta where it empties ito the lake on the south. Another stream feeding the lake from the north is Eski Sigircı Stream. The lake waters flow into Susurluk Stream at Karacabey Through a branch called Karadere arising from the southeast corner and empty into the Sea of Marmara. The lake's shallowness ensures that the waves reach its floor, giving it a continuosly turbid appearance.
The lake surrounded by farmland. Its shores consist alternately of reedbeds and cattails interspersed with grassy meadows.In several areas that are inundated in winter and in spring,beas, corn, melon, and water melon are grown in summer. The willow (salix sp.) is the predominant species of the lake enviroment. The trees, together with the reeds and rushes, provide an ideal enviroment for birds to nest. The 64 ha. willow grove and reedbeds at the mount of Eski Sıgırcı Stream to north of the lake have been an important nesting ground for large variety of birds for a long time. Even the 17th century Ottoman traveler Evliya Celebi mentions this willow grove where birds nest, in his Travel Notes. Location west of Sigirrcık Atik, the willow grove was discovered in 1938 by Prof. Dr. Kurt Kosswig, a former faculty member of the Istanbul University Faculty of Science, who named it "Bird Paradise" due to its importance as a breeding range as weel as taking it under protection of the Faculty of Science. The area was incorporated into the forest regime in 1959 and declared a national park. This well-protected national park was awarded a class A European Diploma in 1976, a status granted by the Council of Europe to those areas in which nature conservation is of the highest quality.