Leaves mostly in 3s, often recurved, linear to lanceolate, 4--15.5 ´ 0.9--1.7(--2.4) mm, margins folded. Inflorescences: staminate spathes subglobose to ovoid, 2.2--4 mm; peduncles abscissing in bud; pistillate spathes linear, 8.5--15 mm. Flowers unisexual; staminate flowers: stamens 9, pedicels briefly remaining attached following anthesis; inner 3 filaments connate proximally, forming column; anthers 1--1.4 mm; pollen in tetrads; pistillate flowers: styles mostly 1.2--2 mm. Seeds fusiform, 4--4.6 mm, base with long hairs. 2n = 48 (Britain). Flowering summer. Waters, mostly calcareous, of lakes and rivers; 50--1600 m; N.B., Ont., Que.; Ark., Calif., Colo., Conn., Del., Idaho, Ill., Ind., Iowa, Kans., Ky., Maine, Md., Mass., Mich., Minn., Mont., Mo., Nebr., Nev., N.H., N.J., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.Dak., Tenn., Vt., Va., Wash., W.Va., Wis., Wyo.; Europe; Asia. I know of no instance in North America where Elodea nuttalli or E. canadensis is weedy. Both are weedy in Europe, and E. canadensis is weedy also in Australia and New Zealand.