This shrew is the largest member of the genus in North America. Truly a water shrew, it swims easily both on the surface and while submerged, mostly by alternate strokes of the hind feet. When leaving the water, it literally springs from the surface.

In Oregon, it occurs in the northern Cascade Range in Clackamas, Hood River, and Multnomah counties, then west in Clatsop, Columbia, and Washington counties along the Columbia River, and southeasterly from Newport through Benton, Lane, Linn, Jackson and Klamath counties. Habitats include alder in riparian zones, skunk cabbage marshes, deep, dark, red cedar swamps, floating mats of yellow cress, and muddy places in both forests and forest edges.