Gresvatnet

 or or is a lake on the border between Norway and Sweden. Most of the lake lies in Hemnes Municipality in Nordland county (Norway) and then a small portion crosses the border into Storuman Municipality in Västerbotten County (Sweden). The lake lies about east of the village of Korgen, and just a few kilometres northeast of the mountain Oksskolten and the Okstindbreen glacier. The lake is one of the upper reservoirs for the Bjerka Hydroelectric Power Station.