Lake Dai, also known by its Chinese name Daihai, is a lake in Liangcheng County, Ulanqab Prefecture, Inner Mongolia, China.

Lake Dai is a round lake with an area of about 160 km (62 sq mi), measuring about 25 kilometers (16 mi) from east to west and about 20 kilometers (12 mi) from north to south. It has an average depth of about 9 meters (30 ft) and a maximal depth of 15–18 meters (49–59 ft).

Under the Qin, Huangqi and Dai lakes formed the northern boundaries of Yanmen Commandery, marking part of the northern frontier of the Chinese empire.

• Li Shizhen (2017), Hua Linfu; et al. (eds.), Ben Cao Gang Mu Dictionary, Vol. II: Geographical and Administrative Designations, Berkeley: University of California Press, ISBN 9780520291966.