The Kerlingardalsá river is of glacial origin. Tributaries include the River Vatnsá and several other streams. Fagridalur is on the west side of the river and Höfðabrekka on the east side. Several thousand fish migrate into this system each season, with the best time to fish being the end of July until mid-October. The amount of sediment in the river is affected by snow and ice melt and sometimes it is possible to see a difference in the river before and after noon. The sediment load decreases as the summer progresses and the river is more easily fished from mid-August, although it is always slightly gray.