Lake Uluabat (Turkish: Uluabat Gölü and Apolyont Gölü) is the name of a freshwater lake in the vicinity of Bursa, Turkey. It is a large lake, covering an area of between 135 and 160 km² depending on the water level, but very shallow, being only 3 m deep at its deepest point. The lake contains eight islands and one other that is sometimes an island and sometimes a peninsula. The largest island is known as Halilbey Island. In the southwest the lake is fed by the Mustafakemalpaşa River, which has formed a silty delta. Water leaves the lake by way of the Ulubat stream, flowing to the west, and reaches the Sea of Marmara via the Susurluk River.
Most shores of the lake are covered in submerged plants, and it has the most extensive white water lily beds in Turkey. Ulubat Lake is one of the breeding areas for the endangered Pygmy Cormorant (Phalacrocorax Pygmeus). The latest DHKD (Society for the Protection of Nature Turkey) survey in June 1998 found 823 pairs of Pygmy Cormorants, 105 pairs of Night Heron, 109 pairs of Squacco Heron, and 48 pairs of Spoonbill breeding on Ulubat.
The alternative name Lake Apolyont comes from the lake's classical name Apolloniatis, from Apollonia-on-the-Rhyndacum , an ancient Greek city situated on its banks which had considerable importance since it was on major trade routes.
Modern residential areas by its shores are Mustafakemalpaşa and Karacabey . The area was famous for centuries for its silkworm cultivation, but this industry has died out due to synthetic fabrics. The main industry today is fishing.