A large clumping wetland grass growing out from short rhizomes and creeping runners, stands up to 120cm in height and will sometimes form a dense sod. The stems are thick with light brown bases that are wrapped in old leaves with a sponge-like texture. The upper leaves are wide and flat, extend longer than the stalk, and are noticeably separated by whiteish knot-like cross walls. The inflorescence is long and cylindrical, carrying both male spikes (4-7 at the top of the stem) and female spikes (2-4 on lower stems).  The fruits are yellow-green or straw-coloured and are inflated and egg-shaped with multiple ribs, narrowing to a beak with two points and three stigmas.