The Suldalslågen has a natural watershed of , of which 75% is above the timber line in high mountain areas, making it western Norway's largest river system. The Suldalslågen and its upstream watercourses are heavily dammed and regulated (including transfer of water across catchment borders) for hydroelectric power generation, and represents about 6% of Norway's total hydroelectric power generation. The upper tributaries of the Suldalslågen are located on the vast Hardangervidda plateau in Odda (in Hordaland county) and Vinje (in Telemark county).