Røsvatnet (Norwegian) or Reevhtse (Southern Sami) is a lake and reservoir in Hattfjelldal Municipality and Hemnes Municipality in Nordland county, Norway.

It has been the site of human occupation since the Stone Age.

Its depth is 240 metres (790 ft), its volume is estimated at 15 cubic kilometres (3.6 cu mi), and its surface elevation is 374 metres (1,227 ft) above sea level.

The 17.39-square-kilometre (6.71 sq mi) island Røssvassholmen is located in the southern part of the lake.

The highest point on the island reaches 206 metres (676 ft) above the lake's surface (at top regulation height).