A new $8 million project at the Bonneville Lock & Dam aims to make it easier for Pacific lamprey to migrate along the Columbia River.
The project, currently under construction on the Washington side of the dam, involves demolishing and redesigning the upper part of the fish ladder.
The ladder is a series of tiered concrete walls, spanning about 800 feet along the side of the dam, that fish can use to go upstream. The troublesome part of the ladder, at least for the lamprey, is known as the “serpentine section.” It features gaps in the concrete walls that create a path along series of sharp S-turns, in fast moving water that fish must navigate in the final leg of the trip around the dam.
The new design will have softer edges and fewer hard angles, making it easier for lamprey to swim through.
“We had many years of research showing that lamprey were really struggling to pass,” said Erin Kovalchuk, project manager with the U.S. Army Corps of Engineers. “That’s when we did the computer modeling and could see how high the (water) velocities were in this old S curve configuration.”
All sorts of fish use the fish ladder, but in particular biologists track the passage of migrating species such as shad (which use the ladders in the greatest numbers), steelhead trout, salmon and lamprey.
In 2024, just under 40,000 Pacific lamprey were counted passing the windows of the main fish ladders, according to the U.S. Army Corps of Engineers. But studies suggest that about half of the lamprey that approach the channel below the Bonneville Dam never go through a fish ladder.
Over the next two years, the Army Corps will track lamprey numbers to see if they’re improving with the new design.
Lamprey are fish, but they aren’t as strong of swimmers as salmon. For one thing, they don’t have paired fins. Their method of swimming upstream involves a kind of “sprint and suck” technique. Lamprey use their suction cup mouths to attach to a rock or the concrete of the fish ladder, gain their strength, then swim forward in a short burst, repeating this method as they go.
“In this S configuration, it was all high velocity, so the lamprey had no resting spot,” Kovalchuk said. “This new design is also going to provide a little bit more slack water.”
In March 2024, the U.S. Army Corps of Engineers added a bypass lamprey flume, to both help the lamprey pass the dam, and to allow them to be collected for a trap and haul program by the Columbia River Inter-Tribal Fish Commission, which aims to restore lamprey populations in Columbia River Basin tributaries upriver. The flume looks like a piece of metal ducting that rises above the fish ladder. Last year, about 34,600 Pacific lamprey used the flume.
“The flume was engineered to give the lamprey a more direct up-and-over shot so they could avoid the serpentine and flow control sections of the ladder,” said park ranger Katie Payne. “There’s just a trickle of the natural river water going through this pipeline. The lamprey get in there, and then they kind of suck and slither their way up and over.”
Construction on the new fish ladder started Dec. 9 and should be complete by the first week of March – just in time for the start of the salmon run in March.
Pacific lamprey migrate a little later, starting in June.
Lamprey and salmon are both anadromous fish – meaning they spend part of their lives in freshwater rivers and part of their lives in the salt water of the ocean – but they’re very different creatures. Pacific lamprey are a primitive fish species that lack scales and are some 400 million years old.
“We find that people love them or hate them; there’s no in between,” park ranger Tyler Ardent said, “but they’re completely fascinating creatures.”
Lampreys are parasitic fish. They don’t have jaws, just a suction cup mouth full of teeth that they’ll use to attach to another fish, then bleed them. They produce an anticoagulant in their saliva so they can drink the blood of their host food. Pacific lamprey don’t generally kill the animal they’re feeding on (unlike the sea lamprey, an invasive species found in the Great Lakes).
“Yes, they’re freaky. Yes, they’re weird,” Ardent said, “but if you’ve been around for 400 million years, you get to be a little weird, you get to be a little freaky.”
The Pacific lamprey can be seen suctioned to the fish viewing windows at the Bonneville Dam visitors center in the summer months, particularly around July.
Those windows at the Washington side visitors center are currently boarded up during the fish ladder construction, but they’ll reopen once that work is complete.
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