Lake Eucumbene is the largest reservoir in the Snowy Mountains Scheme and is the central connection for the northern (Tumut/Murrumbidgee rivers) and southern (Snowy River) halves of the Scheme. The Goodradigbee and Murrumbidgee rivers from Tantangara Dam are connected to the Eucumbene River at Lake Eucumbene via the Murrumbidgee-Eucumbene Haupt-tunnel. The Eucumbene River at Lake Eucumbene is connected to the Snowy River at Island Bend Pondage via the long Eucumbene-Snowy Haupt-tunnel; the longest tunnel in the Snowy Mountains Scheme, with a circular diameter of .