We report optofluidic waveguides made by filling microchannels in aerogel with water. The aerogel cladding is a nanoporous material with an extremely low refractive index of similar to 1.05, giving a large index step from the water core. Channels were formed by removing embedded optical fibers, which could be nonuniform or multiple. The porosity of the aerogel allowed air to be displaced from the channel, preventing the trapping of bubbles. The attenuation of red light in the highly multimode water core waveguide was no greater than 1.5 dB/cm.