Dasymys is a thickset, heavy rodent. Both the hands and the feet have five digits. The toes are fairly short, and the claws are not suited to climbing. The ears are small, rounded, and evenly fringed with hair. The incisor teeth are not grooved.
Females have six mammae.
Although it is reported to occur in forests and savannahs, Dasymys is usually found in wet, grassy areas, such as marshes and reed beds. It is primarily nocturnal but is sometimes active by day. It is basically terrestrial but swims and dives readily. It also establishes distinct runways that radiate from the nest to feeding areas. Dasymys also has been reported to find shelter in holes along the banks of streams.