The Lengguru Fold and Thrust Belt is bounded on the east by the Wandammen Ridge, which is composed of older (Paleozoic and Mesozoic) sedimentary and metamorphic rocks.
[4] The isthmus includes a gap in the chain of mountains that run almost continuously down the length of the island from the Bird's Head Peninsula to New Guinea's southeastern tip.
This gap, known as the Omba-Woromi corridor, extends along the eastern side of the Wandammen Mountains and southeast of the fold and thrust belt, and is about 60 km wide with a maximum elevation of only 160 metres.
It separates the Weyland Mountains, the westernmost portion of New Guinea's Central Range, from the uplands of the isthmus and the western peninsulas.
The lake is drained by the Omba River, which follows the corridor southwards to empty into the Arafura Sea southeast of Etna Bay.