Plants small to large, forming mats, dark green or yellow-green to blackish green; aquatic and saxicolous, in splash zone or submerged. Stems naked and black below when old, suberect, 15-80 mm long, branching irregular above stipe, subfastigiate; in section round to oval, central strand absent, inner cortical cells large, thin-walled, hyaline, in 5 or 6 rows, outer cortical cells smaller, yellowish, thick-walled, in 5 or 6 rows, epidermis absent; axillary hairs not seen; paraphyllia absent; pseudoparaphyllia absent. Leaves evenly spaced, spreading to crect-appressed wet, appressed dry, ± concave; on stipe lanceolate to triangular, 1.5-2.0 mm long; acute; margins plane, entire, eroded; upper stem and branch leaves variable; narrowly or broadly elliptical or short and broadly oblong, 1.2-2.2 mm long; acute to narrowly acuminate or occasionally mucronate to apiculate; rounded at base; margins plane, entire, cells not differentiated. Costa variable, absent, present only at base, present and discontinuous only at apex and base, or single and strong throughout, smooth; ventral and dorsal surface cells elongate; in section flat below, round above, guide cells not differentiated, in best development consisting of 3-6 rows of undifferentiated, thickened cells; most leaves with bistratose region at extreme base and thickened awn at apex. Upper laminal cells linear-fusiform and somewhat sigmoid, homogeneous, 57-89 µm long, 7-10 µm wide, walls thickened or rarely thin, smooth; basal cells linear to long-rectangular, 50-125 µm long, 7-10 µm wide, brownish yellow, walls incrassate, smooth; alar cells strongly differentiated, forming distinct groups, enlarged and inflated, hyaline, walls thin. Dioicous or rarely autoicous. Perichaetia at apex; perichaetial leaves numerous, broadly ovate, apex acute, sheathing below. Seta 4-6 mm long, yellow-brown to blackish, twisted clockwise when dry, smooth, thick. Capsule exserted, erect, short-cylindrical or rarely ovoid, 1.0-2.2 mm long, smooth but somewhat ribbed when young and dry, yellow-brown to black; urn short-cylindrical; neck not differentiated; exothecial cells irregular, rounded to quadrate or hexagonal, walls incrassate, cells at mouth quadrate, darker; annulus not differentiated, neck cells hexagonal to rectangular, thickened; stomata absent. Peristome rudimentary, yellow to orange; exostome teeth irregular, short-rectangular, truncate, erect, 40-50(-95) µm high, smooth with irregular prostome development; endostome absent. Operculum curved-rostrate, attached to columella, persistent, 1.0-1.3 mm long. Calyptra not seen. Spores rounded, 25-31(-37) µm, granulate, brown.
Aquatic and saxicolous, in splash zone or submerged in mountain streams.
Endemic to southern Africa, W. hygrometrica is found in the southwestern Cape. Most specimens have been collected on Table Mountain, fertile ones mostly between October and February.