One of the rivers that almost flow right across the length
of Sikkim is the Teesta (also spelt as Tista). Its
major tributary is the Rangeet, which originates from the Rathong glacier
and meets it at the border between Sikkim and West Bengal. The River Ramam
a tributary of Rangeet, a part of the river Rangeet itself and Rangpo Chu
a tributary of Teesta define the southern border between Sikkim and
Teesta originates from the lake Cholamu where it is hardly a stream. No one can imagine that this innocuous looking stream would transform into a thundering mighty river less than a hundred kilometers downstream. A little further down from lake Cholamu, the river is joined by a stream originating from lake Gurudogmar.
During monsoon, innocuous looking rivers of Sikkim become swollen, swift, muddy and dangerous. The rivers are narrow, serpentine and full of rocks.
Teesta River as it approaches the border between Sikkim and West Bengal becomes quite wide and clear of rocks and it is ideal for Rafting, Teesta finally joins the Bramhputra in Bangladesh.