Fish Active day and night

Pacific Brook Lamprey

Occidentis pacifica

iNaturalist

A hidden gem of Pacific Northwest waterways, this 'living fossil' spends years tucked in the mud before emerging for a spectacular spring dance in shallow gravel streams.

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Quick Identification

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Size

10–17 cm (4–6.7 inches) in length; weight is typically under 50 grams (1.8 ounces).

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Colors

Uniform dark olive, brown, or slate-grey on the dorsal side, fading to a lighter tan, yellowish, or silvery-white belly.

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Key Features

Slender, eel-like body without scales
Seven distinct pore-like gill openings behind each eye
Single dorsal fin with a shallow notch separating it into two lobes
Small, hooded sucker mouth with blunt, non-functional teeth

When You’ll See Them

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Activity pattern Active day and night

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Peak hours Nighttime for migration; daytime for spawning activity

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Season March-July

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Diet Larvae (ammocoetes) are filter feeders that consume microscopic algae, diatoms, and organic detritus. Adults do not eat.

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Habitat Cool, clear freshwater streams with a combination of silty backwaters for larvae and gravelly riffles for spawning.

public Geographic range

Where Does the Pacific Brook Lamprey Live?

The Pacific Brook Lamprey is native to the western coast of North America. Its core range extends from British Columbia in Canada southward through the coastal and inland waterways of Washington and Oregon, reaching as far south as the San Joaquin River drainage in California. They are strictly freshwater residents, primarily found in the tributaries of the Columbia River and various smaller coastal watersheds along the Cascadia margin.

Basemap © OpenStreetMap contributors

2 Countries

450K km² Range

Data Deficient Conservation

US United States CA Canada

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iNaturalist / Verified observation data

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Behavior

The Pacific Brook Lamprey is a secretive, non-parasitic freshwater specialist. For the vast majority of its life—between three to seven years—it exists as a blind, worm-like larva known as an ammocoete. These larvae live buried in the soft silt and organic detritus of stream banks, acting as vital ecosystem engineers by recycling nutrients and aerating the sediment.

Once they reach maturity, they undergo a dramatic metamorphosis during the fall, developing eyes and a functional (though non-feeding) sucker mouth. In the spring, the adults emerge from the mud to spawn. They are known for their communal nesting behavior, where they use their mouths to lift and move small stones to create a shallow depression in the gravel. Unlike their larger relatives, they never travel to the ocean and spend their entire lives within a few miles of where they hatched.

Because they do not feed as adults, their final life stage is focused entirely on reproduction. After a frantic few weeks of spawning in clear, shallow riffles, the adults die, providing a final pulse of nutrients to the stream. They are rarely seen by humans except during this brief spring window when they congregate in shallow water.

photo_camera EverydayEarth exclusive

Camera Tips

Capturing the Pacific Brook Lamprey requires an underwater approach. Use a waterproof action camera or a specialized underwater trail camera capable of high-definition video. The best placement is in shallow, clear-water riffles during the spring (March to June). Look for 'redds'—small depressions in the gravel where stones have been cleared away—as these are active spawning sites. Secure your camera to a weighted plate or a low-profile tripod to keep it stable against the current, and angle the lens slightly upward to capture the lampreys as they wriggle over the rocks.

Lighting is a challenge in stream environments. During the day, position your camera so the sun is behind it to avoid glare on the water's surface, but be mindful of shadows that might spook the fish. For nighttime captures, use a camera with 'No-Glow' infrared (IR) LEDs. Lampreys are sensitive to bright white light, and IR allows you to see their nocturnal movements without disrupting their natural behavior. Ensure your camera is set to record short video clips (15–30 seconds) rather than still photos, as their movement is their most identifying characteristic.

Because these lampreys do not eat as adults, you cannot use bait to attract them. Instead, you must rely on 'structural attraction.' Find an area where the stream narrows or where a natural obstacle creates a small resting pool next to a fast-moving riffle. These bottleneck areas are high-traffic zones during the spawning run. If you have a backyard stream, maintaining a healthy riparian zone with overhanging vegetation will provide the cover they need to feel safe enough to enter your camera's field of view.

Similar Species

Species that look similar or are commonly confused with Pacific Brook Lamprey.

Western Brook Lamprey

Nearly identical in appearance, but can be distinguished by subtle differences in the arrangement of teeth on the oral disc and slight variations in genetic range.

Pacific Lamprey

Much larger (up to 76 cm), parasitic as adults, and migrates from the ocean to freshwater to spawn.

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Frequently Asked Questions

While they move between pools primarily at night to avoid predators, Pacific Brook Lampreys are very active during the day during their spring spawning season, when they can be seen moving stones in shallow, sunlit riffles.

You cannot attract them with food, but you can support them by maintaining a natural, chemical-free stream. Ensuring your creek has a mix of silty banks for the larvae and clean gravel for the adults is the best way to encourage their presence.

Larval lampreys filter-feed on microscopic algae and organic matter from the mud. Once they turn into adults, they stop eating entirely, living off stored fats until they finish spawning.

Yes, they can be found in many suburban and even urban streams in the Pacific Northwest, as long as the water is cool, oxygenated, and the stream bed hasn't been completely paved or channelized.

The Pacific Brook Lamprey is much smaller, rarely exceeding 7 inches, and stays in freshwater its whole life. The Pacific Lamprey is a giant by comparison, reaching up to 30 inches, and is anadromous, meaning it spends its adult life in the ocean.

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