Distribution: Introduced in much of North America; central and western Washington, western Oregon, and California.
Habitat: Ponds and streams, often forming mats.
Flowers: Late June - August
Origin: Introduced from Eurasia
Conservation Status: Not of concern
Aquatic, herbaceous perennials from slender rhizomes, the stems branching, somewhat flattened, 4-8 dm. long and 1-2 mm. broad.
: Leaves alternate, all submersed, narrowly oblong, 3-8 cm. long and 3-10 mm. broad, strongly crisped, finely serrulate on the upper margins, rounded at the tip, sessile and clasping, 3- to 5-nerved; stipules delicate, 4-8 mm. long.
Flowers perfect, in spikes 1-2 cm. long on peduncles 3-5 cm. long; perianth of 4 clawed segments, each with an upturned, oval blade; stamens 4, fused with the claws; pistils 4, sessile.
Achenes ovoid, 3 mm. long, with 3 obtuse but prominent keels, tapered into a beak 2-3 mm. long.
One hybrid, Potamogeton crispus × P. praelongus (= P. ×undulatus Wolfgang ex Schultes & Schultes f.), has been described.