Culms 20–35 cm × 0.3–1 mm. Leaves: apex of distal leaf sheath subacute to narrowly acute, tooth to 0.3(–1.1) mm. Spikelets narrowly lanceoloid, 3–12 × (1–)2–2.5(–4) mm, apex acute; floral scales 25–100, 10–12 per mm of rachilla, orange brown to stramineous, ovate, 1.5–2 × 1 mm, midribs mostly keeled, apex acute or narrowly rounded in proximal part of spikelet. Flowers: perianth bristles 6–7, brown, stout, the longest equaling or exceeding tubercle; stamens 2–3; anthers brown, 0.3 mm; styles 2-fid. Achenes 0.9–1.1 × 0.6–0.8 mm. Tubercles deltoid, 0.25–0.5 × 0.5–0.7 mm, 1/2–2/3 as high as wide, 1/4–1/2 as high and 2/3–4/5 as wide as achene. 2n = 10.

Fruiting summer to fall. Fresh shores, stream beds, pine woods, disturbed places; 0–400 m; Ark., Calif., Kans., La., Mo., Okla., Tenn., Tex.

Some collections of Eleocharis lanceolata from Tennessee appear to be intermediate with E. obtusa. The California record is an introduced rice-field weed collected in 1949.