Mammals Active day and night

Northern Water Shrew

Sorex palustris

iNaturalist Wikipedia

The Northern Water Shrew is nature’s tiny scuba diver, capable of diving to stream bottoms and even running across the surface of the water.

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0 Habitats

Quick Identification

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Size

Length: 13-17 cm (5-6.7 in); Weight: 8-18 g (0.3-0.6 oz)

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Colors

Dorsal side is dark grey to near-black; underbelly is a contrasting silvery-white or light grey

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Key Features

Stiff fringe of silver hairs on the sides of the hind feet for swimming
Long, pointed snout with prominent whiskers
Small, inconspicuous eyes and ears
Velvety, water-repellent fur

When You’ll See Them

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Activity pattern Active day and night

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Peak hours Active in 1-2 hour bursts throughout the 24-hour cycle

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Season Year-round

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Diet Primarily aquatic insects (stoneflies, mayflies, caddisflies), fish eggs, small minnows, tadpoles, and terrestrial invertebrates.

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Habitat Edges of cold, fast-moving mountain streams, lakeshores, marshes, and damp coniferous forests.

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Where Does the Northern Water Shrew Live?

Native to the North American continent, the Northern Water Shrew occupies a vast territory stretching from the wild landscapes of Alaska and across the breadth of Canada. In the United States, its presence is most notable along major mountain corridors and northern border states, extending southward through the Rockies, the Appalachians, and the Sierra Nevada where clean, oxygen-rich water is abundant.

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2 Countries

10.5M km² Range

Least Concern Conservation

US United States CA Canada

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iNaturalist / Verified observation data

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Behavior

The Northern Water Shrew is a high-octane powerhouse of the mammal world. As the smallest mammalian diver, it possesses an incredibly high metabolism that requires it to hunt almost continuously, day and night. It is a solitary and fiercely territorial creature, spending its life in a cycle of frantic foraging followed by short periods of deep sleep. Its most remarkable trick is its ability to 'run on water'; by trapping air bubbles in the stiff hairs of its feet, it can generate enough surface tension to skitter across a pond's surface without sinking.

In the water, these shrews are surprisingly agile. They use their large hind feet as paddles to dive to the bottom of streams and ponds in search of prey. Because their thick fur traps so much air for insulation, they are extremely buoyant and must swim vigorously to stay submerged. While they are rarely seen by humans due to their small size and rapid movements, they are vital indicators of clean, unpolluted water sources.

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Camera Tips

Capturing a Northern Water Shrew on camera requires precision and a focus on 'micro-habitats.' Because of their tiny mass, they often fail to trigger standard PIR (Passive Infrared) sensors on budget trail cameras. To increase your chances, look for 'shrew highways'—naturally occurring bridges like fallen logs that cross small streams or mossy rocks at the water's edge. Position your camera just 4 to 6 inches above the ground, aimed directly at the surface of these transit points.

Standard photo mode often results in a blur due to the shrew's rapid, twitchy movements. Instead, set your camera to high-definition video mode with the highest possible frame rate (at least 30fps, though 60fps is better). This allows you to witness their unique swimming and diving behaviors in slow motion. If your camera has a 'close focus' or macro lens attachment, now is the time to use it, as the best shots are usually taken from less than three feet away.

While they are active 24/7, ensure your camera has a fast-recovery infrared flash for night captures. They are extremely sensitive to scent; avoid touching the camera or the surrounding area with bare hands. Baiting is rarely necessary if you find a high-traffic stream bank, but a small amount of fish-based cat food or mealworms placed on a flat rock in front of the lens can pause their frantic movement long enough for a clear shot. Check your footage frequently, as these little dynamos can fill an SD card with activity in a single night.

Similar Species

Species that look similar or are commonly confused with Northern Water Shrew.

Marsh Shrew

Found specifically in the Pacific Northwest, it is darker and lacks the high-contrast silver belly of the Northern Water Shrew.

American Pygmy Shrew

Much smaller (one of the smallest mammals in the world) and lacks aquatic adaptations like fringed feet.

Cinereus Shrew

Also known as the Masked Shrew, it is much smaller, more brown than black, and lacks the specialized swimming hairs.

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Frequently Asked Questions

Northern Water Shrew are active day and night throughout the year. They operate on a 'burst' schedule, foraging for about an hour and then sleeping for an hour to fuel their intense metabolism.

To attract them, you must have a clean water source like a stream or pond with plenty of cover, such as rocks, logs, and native riparian plants. They avoid open areas where they are vulnerable to predators.

They are insectivores that specialize in aquatic prey. They dive to find stonefly and mayfly larvae, but will also eat small fish, tadpoles, and earthworms found near the water's edge.

They are rarely found in typical suburban yards unless the property borders a wild, permanent stream or wetland. They require high water quality and are sensitive to urban pollution.

Look for the size and the feet. The Northern Water Shrew is significantly larger than the common Masked Shrew and has distinct, stiff silver hairs fringing its hind feet for swimming.

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