There are many nice swimming spots in Hemsedal. Small mountain lakes are rapidly heated on a warm summerday (easily up to 20 C). The water in rivers and streams is a bit colder, especially in early summer when the snow is melting.
Following spots are recommended:
Grøndøla, river in Grøndalen near the golf course
Hemsila river, flowing through Hemsedal centre, behind Rampa shopping centre
Rjukandefossen, is a beautiful spot for swimming, you find it 100 meters down the river, south of the suspension bridge. Swimming close to the waterfalls is forbidden due to very strong currents.
Grytevatnet, is a calm water in the forest on the way to Lykkja. Drive towards Lykkja. Just before parkinglot Hestanåni, take to the right and follow the road and hold to right in the next crossing. When you see the lake, prak you car along the road and jump in!
Nøsen, by the Panorama road (ca 25 min drive form Hemsedal)