They are of glacial origin.
How are lakes formed by glaciers in the mountains?
Most of the freshwater lakes are in the Himalayan region. They are of glacial origin. They are formed when glaciers dug out a basin, which was later filled with snow melt. These lakes can form directly at the head of retreating glaciers, buffered by big piles of rock debris that the glacier has carried down, called terminal moraines, which signal the glacier has gone as far as it can go.