Sarez Lake is a lake in Rushon District of Gorno-Badakhshan province, Tajikistan. Length about 75.8 km, depth few hundred meters, water surface elevation about 3,263 m over sea level and volume of water is more than 16 km³. The mountains around rise more than 2,300 m over the lake level.
The lake formed in 1911, after a great earthquake, when the Murghab River was blocked by a big landslide. Scientists believe that the landslide dam formed by the earthquake, known as the Usoi Dam, is unstable given local seismicity, and that the terrain below the lake is in danger of catastrophic flood if the dam were to fail during a future earthquake.
Shadau Lake is a small water body southwest of the Usoi Dam and west of Sarez Lake
The 1911 Sarez earthquake, estimated at 6.5-7.0 on the Richter scale, occurred about midnight, 5-6 February, 1911 (old style). Deaths were estimated at 302. The landslide was 2.2 billion cubic meters and formed the Usoi Dam which is approx. 5km long, 3.2 km wide and up to 567m high, the tallest natural dam in the world. Usoi was a village buried under the landslide. It was not until April 1914 that the lake rose high enough to begin flowing over the dam. The lake reached its current level in 1920. The area was so isolated and the destruction of mountain tracks so complete that it took six weeks before word reached the Russian posts at Murghab and Khorog.
In 1968 a landslide caused two-meter-high waves in the lake. A 1997 conference in Dushanbe concluded that the dam was unstable and might collapse if there were another powerful earthquake. A 2004 study by the World Bank held that the dam was stable. The principal danger seems to be a partially detached mass of rock of about 3 cubic kilometers that could break loose and fall into the lake. Since the valley below the dam is so narrow, any flood would be very destructive. The result of a global risk analysis carried out by STUCKY for the World Bank was presented at the 2002 IAHR Symposium in St Petersburg and at the 2006 International Congress on Large Dams in Barcelona