| Map: |
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| Subdivision Type1: | Country | ||||||
| Subdivision Name1: | Norway | ||||||
| Subdivision Type2: | County | ||||||
| Subdivision Name2: | Nordland | ||||||
| Subdivision Type3: | Region | ||||||
| Subdivision Name3: | Helgeland | ||||||
| Subdivision Type4: | Municipalities | ||||||
| Length: | 163km (101miles) | ||||||
| Source1: | Simskardvatnet | ||||||
| Source1 Location: | Hattfjelldal Municipality, Nordland, Norway | ||||||
| Source1 Coordinates: | 65.2831°N 13.8142°W | ||||||
| Mouth: | Vefsnfjord, Mosjøen | ||||||
| Mouth Location: | Vefsn Municipality, Nordland, Norway | ||||||
| Mouth Coordinates: | 65.8358°N 13.1906°W | ||||||
| Basin Size: | 4122km2 | ||||||
| Tributaries Left: | Svenningelva | ||||||
, [1], or [2] 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 Hattfjelldal Municipality, Grane Municipality, and Vefsn Municipality. 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 the town of Mosjøen, the river discharges into the Vefsnfjorden. The Laksforsen waterfall lies along its course.
Historically, it was an important salmon fishery, but it has now been infected with the salmon parasite Gyrodactylus salaris.[3]