Stoloniferous aquatic perennial; culms decumbent, often only the inflorescence emergent, to 120 cm high overall. Leaves glabrous, scabrous; blade flat, to 17 cm long and 1–4 mm wide; ligule acute, 5–11 mm long. Inflorescence a slender, rather sparse panicle, to 25 cm long. Spikelets 4–6-flowered, 12–19 mm long (excluding awns), green or faintly tinged purple; glumes obtuse to acute, the lower 1–3-nerved, 3–4.5 mm long, the upper 3–5-nerved, 4–6 mm long; lemma 6–8.2 mm long, scabrous along nerves in upper part, otherwise mostly smooth, apical teeth 2 or 4, the outer pair smaller and lower when present, the inner pair 0.3–1 mm long; awn 14–26 mm long, inserted 35–50% of the lemma length from the apex, column and bristle not distinguished; palea slightly shorter than lemma. Flowers Oct.–Mar.