Thalay Sagar is one of the mountains in Gangotri group of peaks in Western Garhwal Himalaya in the state of Uttarakhand. It is on the main ridge that lies near the Gangotri Glacier and is one of the difficult peaks to access. Thalay Sagar lies ten kilometers southwest of the sacred Hindu site, Gaumukh.

It rests near the Jogen group of peaks and has the Kedar Tal lake at its peak. It is situated at an altitude of 6,904 metres (22,651 feet) above mean sea level. The geographic cooordinates of the mountain are 30°51`29?North, 78°59`50?East. The mountain prominence ( it is a measure of vertical separation between mountains) of Thalay Sagar is 1,000 metres (3,280 feet).