Between Iznik and Orhangazi districts of Bursa. A freshwater lake formed by tectonic movements. The main sources of nutrition of the lake are the Samanli Mountains in the north and the mule mountains in the south. Karadere and Sölüz Creek are the largest rivers that feed the lake. 298 square kilometers in area, 32 square kilometers in length. The widest part of the lake is 11 kilometers, its deepest point is about 65 meters.
Lake Iznik has the most carp; marrow fish, freshwater perch and other types of silver fish. Crayfish obtained from the lake is also exported, providing an important source of income to the region. Lake Iznik has important bird area status. It is home to birds such as small balaban, twilight heron, paddy, erguvan heron, angite, Hungarian duck, snake eagle. Cormorant, blackhead gull, bahri, greenhead and applehead patka are the most common species. The lake is also an important breeding ground for paddy, small white heron, small balaban and night heron. The lake, which birds do not prefer in winter, only gains importance when the wetlands in Central Anatolia freeze.
In spring, when viewed from a high point of view, the blue lake and the surrounding orchards offer a spectacular colour fulfilment. It is also rumored that the blue of the lake inspired Iznik tiles. There are many historical buildings from the Roman and Byzantine periods around Lake Iznik.