Lake Sarez is a turquoise lake 55 kilometres long in the Pamir mountains of Tajikistan, in the Gorno-Badakhshan region, made in one night in February 1911 when an earthquake dropped a mountainside across the Murghab river and dammed it with the Usoi landslide, the tallest natural dam in the world, and it is reached on foot by a trail that crosses the river twice on swaying cable bridges. The landslide buried the village of Usoi and its people, and as the water rose behind the rubble over the years it drowned the village of Sarez upstream, which had survived the earthquake; the dam is 567 metres high, taller than any dam humans have built, and it holds back seventeen cubic kilometres of water that the whole region watches, since a failure would send a flood down the Bartang and the Panj into Afghanistan and Uzbekistan and reach the Aral basin, and a monitoring station and warning system have been installed on the crest. Visits need a permit, and the walk in follows the Bartang valley from the last village, past the bridges, to the barren rockfield near the dam crest where most visitors sleep out and take the lake at first light.
The lake at dawn is the reward: a sheet of turquoise running east between bare brown walls of 4,000 and 5,000 metres, with nothing on its shores. Crossing the crest of the Usoi dam means picking a path over loose, sun-baked rockslide, with the lake held on one side and the empty gorge of the Murghab dropping away on the other, and a small motorboat kept by the monitoring station is the only way to cover any of the water, running along the walls to bays where the drowned valley shows in the shape of the shore. The Bartang valley below is one of the most remote inhabited valleys of the Pamirs, with stone villages and terraces, and the Pamir Highway is the road that gets close. Lake Sarez is a lake made in a night, and the mountain that made it is still holding.