Great Blue Hole
The Great Blue Hole is a giant marine sinkhole off the coast of Belize. It lies near the center of Lighthouse Reef, a small atoll from the mainland and Belize City. The hole is circular in shape, across and deep. It was formed during several episodes of quaternary glaciation when sea levels were much lower. Analysis of stalactites found in the Great Blue Hole shows that formation took place 153,000; 66,000; 60,000; and 15,000 years ago. As the ocean began to rise again, the cave was flooded. The Great Blue Hole is a part of the larger Belize Barrier Reef Reserve System, a World Heritage Site of the United Nations Educational, Scientific and Cultural Organization (UNESCO).
Blue Lake (New South Wales)
The Blue Lake is one of only four cirque lakes found in mainland Australia. The other three, Cootapatamba, Albina, and Club, are shallower and are held entirely by terminal moraines. Blue Lake's valley contains the best-developed glacial features in the Kosciuszko National Park alpine area of New South Wales. It was recognised as a wetland of international importance on 17 March 1996 when a area, comprising the lake and its surrounds, including nearby Hedley Tarn, was designated Ramsar Site 800 under the Ramsar Convention on wetlands. The lake lies within the Australian Alps National Parks and Reserves.