Located in the northwest of the country, Thac Ba lake of Yen Bai province, which is likened to "Ha Long on the mountain" is one of the three largest artificial lakes in Vietnam formed when building Thac Ba Hydropower Plant. The lake is located in two districts of Yen Binh and Luc Yen. The lake covers nearly 20,000 hectares of water surface, including more than 1,300 large and small green islands, and a beautiful cave system hidden deep in the limestone mountains.