The river Vefsna ( or ) is the largest river in Nordland county, Norway. It is long and drains a watershed of . Its headwaters lie in the mountains of Børgefjell National Park at the lake Simskardvatnet. The river runs through the municipalities of Hattfjelldal, Grane, and Vefsn. The southern parts of the river are sometimes called the river Susna. The river flows north, not far from the Swedish border, and some of the minor tributaries come from Sweden. At Mosjøen, the river discharges into the Vefsnfjord. The Laksforsen waterfall lies along its course.