Waterton Lake is a mountain lake in southern Alberta, Canada and northern Montana, USA. The lake straddle the Canada/United States border. The lakes lie in the Waterton Lakes National Park while the upper lake is partly located in the Glacier National Park. In 1979, UNESCO established the Waterton Biosphere Reserve to protect the diverse habitats including prairie grasslands, aspen parkland, subalpine forests, alpine tundra and freshwater fens that surround the lake.. The Waterton-Glacier International Peace Park was inscribed as a World Heritage Site by UNESCO in 1995. The upper and middle Waterton Lake system has a surface of 10.1 km² (3.9 sq mi), while the lower lake has 1.5 km² (0.6 sq mi) and lies at an altitude of 1,274 m (4,180 ft).