This animal is dark grey in colour with lighter underparts with a long tail. Air bubbles are trapped in the thick fur when the animal dives underwater. Its feet have a fringe of hairs, more visible on the larger hind feet, which allow this animal to run on the water's surface. Its body is about 15 cm in length including an 8 cm long tail and it weighs about 13 g.
It swims well and makes short dives in search of food. Its diet includes aquatic insects, small fish, tadpoles, slugs and snails. It is thought to use echolocation to help find prey. Predators include hawks, owls, snakes, mustelids and large fish.
This animal is active during the day but are more active at night. It is generally solitary and territorial except during mating. The female has 2 to 3 litters of 5 to 7 young in a nest in a tunnel or under a log. Water shrews typically live about 18 months.