Isthmohyla rivularis

Males grow to 34 mm (1.3 in) and females to 37 mm (1.5 in) in snout–vent length.^[4] The snout is moderately short and acutely rounded. The tympanum is barely discernible. The fingers have large discs and are up to one-third webbed. The toes have discs that are slightly smaller than those on the fingers and are two-thirds webbed.^[5] The dorsal color varies from grey to light brown. Most specimens have a thin, dark line running through the eye. Other dark markings are variably present. The flanks are usually yellowish, but may in some individuals appear greenish or bluish.^[4] The iris is bronze and has black reticulations.^[4]

Isthmohyla rivularis is found along or in clear streams in lower and premontane rainforests at 1,210 to 2,040 m (3,970 to 6,690 ft). Males call from vegetation by or overhanging fast-moving streams. The tadpoles develop in streams.^[1]

This species was formerly common in parts of its range, but has since strongly declined. The decline is probably caused by chytridiomycosis. Also habitat loss caused by agriculture and selective logging have impacted the species.^[1]