The pelage is thick and not as soft as that of allied genera. The upper parts are dark olive brown, grayish, or blackish, often with a buffy wash, and the underparts are whitish. The tail is fully haired. The outer corner of each incisor projects downward as a sharp point, and the cutting edges of the two upper incisors form an inverted V .
Females have six mammae.
Fish-eating rats frequent streams and swampy areas from 600 to 2,800 meters in elevation. Much of their former range is now under cultivation. While some small fish are taken, crabs and insects seem to be more important parts of the diet. Food is captured by sweeping the vibrissae through the water until contact is made, then seizing or pinning down the prey with the forepaws, and finally biting repeatedly with the sharp incisors. The Johns Hopkins University Press.