Cyrtandra rivularis is a shrub typically growing between 0.5 and 2 meters tall. The stems are many-branched, with a rounded to angular shape, and are covered with multicellular hairs or can be glabrate. Its leaves are simple and opposite, located on the upper 3–4 nodes, with each pair being unequal and asymmetrical. The leaves are elliptic, sometimes broadly so, measuring 6.3–21 cm in length and 1.8–6.8 cm in width, featuring an acuminate apex and a cuneate to attenuate base. The upper surfaces of the leaves are sparsely to moderately appressed hirtellous, while the lower surfaces are moderately to densely covered with rust-colored, velvety, short-pilose hairs; the leaves are thick and chartaceous with serrulate to occasionally serrate margins. The flowers occur in umbelliform cymes of 2–5, emerging from the leaf axils, and are short-pilose throughout. The peduncles range from 14–32 mm long, with pedicels extending from 10–15 mm, elongating to 15–25 mm during fruiting. The calyx is nearly actinomorphic (radially symmetric), greenish-white, 8–12 mm long, extending up to approximately 15 mm in fruit, with narrowly deltate lobes. The corolla is typically bilabiate and white, with a subcylindrical tube flaring slightly at the mouth and lobes broadly rhombic to rhombic-orbicular. It has five stamens, with the upper two fertile and the others staminodial. The ovary is superior, oblong-ovoid, and 1-celled with parietal placentation. The fruit is a white, fleshy, or firm berry, ovoid in shape, 1.3–2 cm long, and often tipped with a persistent stylar beak. It contains numerous ellipsoid, minute seeds with a 0.4-0.5 mm long reticulate surface. It is found in wet forest habitats between 250-670 meters, with a more typical range of 520-670 meters.