[2] The Sen belongs to the upper stretch of the Vilyuy basin.

It begins in an area of small lakes of the upper Vilyuy Plateau.

In its lower course the Sen bends again southwards meandering strongly in a floodplain with oxbow lakes.

The confluence is almost opposite the mouth of the Ulakhan-Vava in the facing bank.

The river freezes between mid October and late May or early June.