Entirely submersed; rhizomatous. Stems to 180 cm long, much-branched, ± 4-angled. Leaves sessile, c. 1.5-6-(8) cm × 4-8-(12) mm, linear-oblong, obtuse, conspicuous nerves 3, widely spaced, usually with 2 finer submarginal nerves, margins ± crimped, usually with minute teeth especially towards tip, translucent, occasionally reddish; stipules 3-5 mm long, membranous, delicate and soon deteriorating to fibres. Peduncles 3-5 cm long, terete, often recurved. Spikes 0.5-1 cm long, few-flowered. Achenes to 4 mm long, including prominent curved beak ± = body, dark olive, flattened on sides, keel ± denticulate, lateral angles obscure.