Lake Teletskoye (Russian: Телецкое озеро, Altay: Алтын Кӧл, Altyn-Köl, literally: "Golden Lake") is the largest lake in the Altay Mountains and the Altai Republic, Russia, and has depth up to 325 meters. Situated at a height of 434 m (1,424 ft) above the sea level, the lake is 78 km (48 mi) long and 5 km (3.1 mi) wide and lies between the mountain ridges Korbu and Al-tyntu, on the junction of the Sailughem Mountains and the Western Sayans. Its surface area is 233 km2 (90 sq mi); however, due to its considerable depth (325 m, 1,066 ft), the lake contains no less than 40 km³ (9.6 cubic miles) of fresh water.
Annual water level fluctuations are estimated at some 348 sm. The lake transparency is high, with the visibility of the lake water ranging from six to fourteen meters. About 70 rivers and 150 temporary streams flow into the lake, the largest of them, Chulyshman River, supplying more than half of the lake's water. The lake is drained through a single outlet, the Biya River, which, after its confluence with the Katun River, forms one of Siberia's largest rivers, the Ob River.
The lake is surrounded by mountains of 600-1,300 m in the northern part and about 1,700-2,400 m (5,600 - 7,900 ft) in the southern part. Lake Teletskoe is included into Altaisky Nature Reserve. That reserve along with the Katun Natural Reserve and the Ukok Plateau Nature Refuge were listed as one of UNESCO World Natural Heritage Sites under the name "Golden Mountains of Altai".