Aquatic herb, 0.5-1.5 m tall; culm often aerenchymatous, several-sided at base, becoming 3-sided above, with creeping rhizomes. Leaves to 40 cm long and 3.5 cm wide, usually minutely scabrid, the veins usually 5 or more. Inflorescences terminal or axillary, branched; spikelets oblong to lanceolate, 4-7 (10) mm long; scales scabridulous and sparsely hispidulous, the keel strong, 3-ribbed, extending into an awn, the scale being shed with achene at maturity, the outer bristles filiform, the inner bristles thin, obovate, caudate at apex, enveloping the achene; stamens 3; style trifid. Achenes trigonous, broadly elliptic, light brown, smooth, to 1.3 mm long including their slender apex. Croat 5340. Abundant at the edge of the lake, usually growing in shallow water or on tree stumps. Flowers and fruits throughout the year.