They have dense fur, blackish but slightly paler or white on the underparts. The longer hairs in its coat, instead of being rounded, as in terrestrial shrews, are grooved on each side, and the grooves contain numerous ridges. This configuration helps trap air, providing the coat with water-repellent properties and increased insulation to counter heat loss while submerged. The long tail is finely furred. The hind feet are wide, webbed, and have fringed or stiff hairs, which act like paddles and aid in swimming.

They prefer small, cold mountain streams with thick overhanging vegetation; however, can also be associated with rivers, lakes, and bogs. They eat aquatic insects, such as mayfly, stonefly, and caddis fly, including larvae and nymphs, but may also eat terrestrial invertebrates as well. American Water Shrews can actually run across water for short distances. Air becomes trapped in their dense fur and the stiff hairs on their feet can hold tiny air bubbles allowing the surface tension of the water to support the shrew's body weight.