Cap 2.0-6.0 cm broad, convex at first, the margin often hung with veil fragments, becoming broadly convex, nearly plane with a low umbo in age; surface lubricous when moist, otherwise dry, cream to cream-buff, the disk slightly darker, smooth to innately fibrillose, often with a scattering of appressed, small ochraceous-brown scales; flesh thick at the disk, thin at the margin, white to cream, unchanging; odor and taste mild.
Gills adnate to subdecurrent, moderately broad, close, pallid becoming medium purple-grey, mottled in age.
Stipe 5-13 cm broad, 0.3-0.8 cm thick, slender, spindly, often twisted, solid at first but with a thin, hollow core at maturity; equal to slightly enlarged at the base, the latter with stiff buff-colored hairs; surface dry, concolorous with the cap, faintly longitudinally striate at the apex, satiny below or with sparse brown fibrils; flesh cream, unchanging; veil pallid, fibrillose-membranous forming an evanescent superior, torn annulus or leaving fragments on the young cap, becoming purple from adhering spores.
Spores 12-15 x 6-7.5 µm, elliptical smooth, with a faint apical pore; spore print purple brown.
Scattered to gregarious in grassy areas, along roadsides, trails, occasionally in wood chips; fruiting from mid to late winter.
Stropharia riparia is recognized by a cream-buff cap, decorated with veil fragments when young, and a slender, typically twisted stipe. A larger, more robust cousin is Stropharia ambigua. Although similarly colored, its cap is more conspicuously appendiculate, and it fruits in natural woodlands as opposed to grassy areas and woodchips. Agrocybe praecox is a look-alike which also fruits in wood chips but has brown, not purple-brown spores and usually a membranous, intact (not torn) ring. Despite its species name, Stropharia riparia is seldom found near water-courses in our area.