The Vefsna is the largest river in Nordland county, Norway. It is 163 km long and drains a watershed of 4,122 km². Its headwaters lie in the Børgefjell mountains and it forms the border between Norway and Sweden for part of its course. It runs through the municipalities of Hattfjelldal, Grane and Vefsn and at Mosjøen it discharges into the Vefsnfjord.
The Laksforsen waterfall lies on its course.