Kaptai Lake is a man made lake in south-eastern Bangladesh. It is located in the Kaptai Upazila under Rangamati District of Chittagong Division. The lake was created as a result of building the Kaptai Dam on the Karnaphuli River, as part of the Karnaphuli Hydro-electric project. The Kaptai Lake's average depth is 100 feet (30 m) and maximum depth is 490 feet (150 m).

Construction of the reservoir for the hydro-electric plant began in 1956 by the Government of East Pakistan. As a result, 54,000 acres (220 km²) of farmland in the Rangamati District went under water and created the lake. The hydro-electric project was funded by the United States. The project was finished in 1962. International Engineering Company and Utah International Inc. received the contract for construction of the dam. The dam is 670.8 meters long, and 54.7 meters high. The dam has a 745 feet (227 m) long spillway containing 16 gates. Through the spillway 5,250,000 cu ft/s (149,000 m³/s) of water can pass. The land that went under water as a result of the dam construction, was 40% of the total arable land in the area. Along with that, 29 square miles (75 km²) of the Government-owned forest, and 234 square miles (610 km²) of other forest land went under water. About 18,000 families with a total of almost 100 thousand people were also displaced. The palace of the king of the Chakmas was also flooded and is now under water.