Linn County ‘fish ladder’ repair speaks to broader aquatic effort

CENTRAL CITY — The Pinicon Ridge Park Dam is getting a touchup this fall to preserve the ecological benefits from its recent restoration.

Linn County Conservation, in partnership with the Iowa Department of Natural Resources, intends to hire a contractor later this year to make repairs to the “fish ladder” on the dam’s west side immediately below the Main Street bridge in Central City.

The feature — first installed in 2023 as part of the Pinicon Ridge Park Dam modification project — includes a series of ascending, water-filled pools that allow migratory fish to travel upstream without being stopped by dams or other barriers.

During the installation, construction crews created the aquatic passageway by strategically placing large boulders throughout the area to slow down the flow of water in a stair-step pattern to create the ascending pools.

High water from this year’s increased rain tested the relatively new structure, however, and some of those boulders have now shifted — necessitating the upcoming repair.

“You never really know what the river is going to do,” Linn County Conservation Deputy Director Daniel Gibbins said. “With these kinds of modification projects, you design them the best you can … and then you wait for a couple floods to see how it all reacts” before making adjustments.

Gibbins said the plan is to hire a contractor this fall or early winter to go in with an excavator to re-situate the boulders that have moved and add in some larger boulders as well to reduce the risk of dislocation during future major rainfalls.

The project should be relatively quick, he said, with an estimated cost around $20,000 — 90 percent of which will be funded by the Iowa DNR. However, its purpose and impact speak to a larger effort to protect and restore Iowa’s waterways.

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Project touts ecological, recreation benefits

The $3.4 million Pinicon Ridge Park Dam project began in 2022 as a way to modify the low-head dam first built there in 1967.

Low-head dams — also called roller dams — are dangerous to boaters, swimmers and tubers because of the powerful recirculating hydraulics created by the dams’ design. They also block wildlife passage, which spells trouble for certain native fish and mussel species.

As a result, there’s been a statewide push in recent decades to address those issues through modification projects like the one completed in Central City — which saw the dam modified and lowered to eliminate the “swirling water” effect known to ensnare debris and people.

The project also included the creation of the fish ladder, as well as splash pools on the east side of the river to allow for safe paddling.

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“Our goals were, in order of importance, solve the safety issue, solve the ecological issue … and create an area that’s a little better for recreation,” Gibbins said. “We feel like the project was really successful for all three.”

The site now attracts throngs of aquatic recreation enthusiasts to the Wapsipinicon River, Gibbins said, as well as supports a diverse ecological mix of birds, bugs, fish and other aquatic wildlife.

He said conservation staff have plenty of anecdotal evidence of fish using the ladder to swim upstream, but that the department intends to work with the DNR in coming years to identify the true quantifiable impact.

‘Fish ladders’ part of growing statewide trend

The Central City fish ladder is one of two such structures in Linn County-managed waterways and one of a handful within the Cedar Rapids-Iowa City Corridor.

Iowa DNR interior rivers research biologist Greg Gelwicks said the structures gained popularity in Iowa roughly 15 years ago as biologists and the public learned more about the migratory habits of Iowa’s fish and mussel species.

“It used to be that people thought it was just fish like salmon that migrated, but we’ve since learned that there’s a lot of other fish that need to make movements up and down rivers and streams throughout their life,” Gelwicks said.

Take smallmouth bass, for example. The top predator in many Iowa rivers, smallmouth bass are a favorite among the state’s anglers and widely recognized as one of the state’s most important game fish species.

Each spring when water temperatures begin to rise, smallmouth bass in Iowa’s larger waterways will move upstream to find smaller, shallower tributaries for spawning. That process is interrupted, however, when the fish meets a dam or other barrier.

“With a lot of those barriers, fish can move downstream over those structures, but once they do, they can never move back upstream again,” Gelwicks said. “So that can create whole sections of a stream that don’t have a particular species or where they don’t do as well as they should.”

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One solution is fish ladders — which allow fish a way to move back upstream by working their way through a series of shallower, ascending pools.

Experts most commonly refer to those features and others that assist in aquatic migration as “fish passage structures” to better account for the wide variety of designs used depending on the given waterway, surrounding geography and targeted species.

Early aquatic passages in Iowa tended to be modeled after similar structures that had gained popularity in places like Oregon or Washington, Gelwicks said, where ladders have been installed with a focus on assisting the annual salmon migration.

Iowa has a very different built environment, however, and a very different aquatic population. As such, adjustments were needed to truly turn the passage structures into effective tools for Iowa’s waterways.

As one of the more recent projects, the Central City fish ladder shows off some of those adjustments through its use of shallower pools and smaller drops than those found in Western waterways.

Efforts to repair the structure should be complete by the end of the year, depending on water levels falling enough to safely complete the work.

Comments: grace.nieland@thegazette.com