Lake Sarez, 60 km long and containing an estimated 17 cubic km of water is quite young. It was formed after an earthquake of colossal proportions on 18 February 1911 in which two cubic kilometres of rock were dislodged, burying Usoi village and blocking the Murghab River.
The resulting Usoi Dam holds back the lake, at least until the next earthquake of such a magnitude. Soviet scientists were aware of the potential for a natural disaster of epic proportions here and studies continue today to monitor the condition of the natural dam, one of the largest in the world. Special permission is required in advance to visit the region of the lake.
South of Lake Sarez in the Alichur river valley is the picturesque Yashikkul Lake ("Blue Water"). This trek begins in the Gunt valley not far from Khorog and passes through high mountain summer pastures – be sure to accept the curds and local bread when it is offered to you by the generous hill folk. From Lake Sarez there is a gradual ascent to a string of upland lakes, allegedly good for trout fishing, before the route descends to Yashikkul and Bulunkul lakes and the Pamir Highway.