Tsomgo Lake (also called Changu Lake or Tsongmo Lake) is a large lake in the East Sikkim district of the Indian state of Sikkim. Etymologically "Tso" means lake and "Mgo" means head, thus literally meaning "source of the lake" in the Bhutia language. The cerulean lake is about 40 kms away from the capital Gangtok at an altitude of 3,780 m (12,400 feet). It is oval-shaped, with a length of about one kilometre and has an average depth of fifteen metres. The tarn with its refulgent waters is situated on the Gangtok-Nathula route.

Tsomgo Lake is declared a sacred lake by the local Buddhist and Hindu population. During the winter months, the lake freezes over. It is fed by the melting snow during the summer months from May to August. Flora around the lake includes the rhododendron, the state tree, primulas, iris and poppies. The Brahminy ducks, red panda and migratory birds frequent the lake. Due to the heavy promotion of tourism in the state, many locals have set up shop here offering yak rides, yak cheese, trinkets, and local curios.
Source: wikipedia

The best time to visit the lake is between the March to late May and October to Mid-December. Inner Line Permits are required by tourists the visit the lake since it is a restricted area. Tourists can obtain these permits from local travel agents in Gangtok by signing up for a tour of a minimum of two people as individual travelers are not given the permit.