Isteren is a lake in Engerdal Municipality in Innlandet county, Norway. The lake lies to the southwest of the large lake Femunden and about northwest of the village of Drevsjø.
Isteren is a lake with a large diversity of species. It is a popular fishing area, and the chances for the good catch is certainly present. In the summer of 2006, a trout weighing was caught with a rod from a small boat. It is also rich in whitefish, pike, perch, grayling, burbot and herring. Around the lake there are two fish mounds and some single cabins.
The river SømÃÂ¥a, originating from lake Langsjøen, flows into Isteren from the north. It is a river with a rich bird life, especially in the spring. Here one can observe rare species of migrating birds.