Atelopus nahumae (San Lorenzo harlequin frog) is a species of toad in the family Bufonidae. It is endemic to Colombia and only known from humid montane forest of Sierra Nevada de Santa Marta in the Magdalena, La Guajira, and Cesar Departments.
Adult males measure 32 to 37 mm (1.3 to 1.5 in) and females 45–51 mm (1.8–2.0 in) in snout–vent length. The snout is acuminate or sub-acuminate. The tympanum is absent. The fingers have traces of basal webbing while the toes are fully (toes I to III) to partially webbed (toe IV). Skin is dorsally smooth but bears granules, small conical tubers, and small warts. Dorsal coloration is dark or light brown, with our without spots. There is a brown X-mark in the supra-scapular area. Some specimens have a dark-brown mid-dorsal line.