Pinicon Ridge Park Dam Modification Project

Pinicon Ridge Park Dam

The Linn County Conservation Board owns the low-head dam in Central City. The dam was built in 1967 on the Wapsipinicon River downstream from Pinicon Ridge Park, just east of Highway 13. The dam surpassed its expected 50-year life.

Initiatives to modify low-head dams have been taking place throughout Iowa to not only improve the water quality of rivers and streams, but to improve safety, increase the environmental health and population of aquatic life in the river, and to provide recreational opportunities. 

Linn County Conservation studied the issue for several years, held public input sessions, including providing online materials during the Covid-19 pandemic from staff and professionals in the field about possible concepts to address the priorities of this modification. The Conservation Board accepted a bid on a dam modification project, which began in December, 2022.

Virtual Tour

Take a virtual tour of the dam modification construction site, and observe the progress of the project over time.

Project Highlights

  • The dam was not removed, but rather lowered 12-18 inches from the top.
  • Boulders and other engineered materials were placed downstream to allow fish and paddle sport passage.
  • The "swirling water" effect which traps debris and people below a roller dam has been eliminated. 
  • Due to low water levels along the Wapsipinicon River during the spring and summer, the dam modification project was completed in June of 2023 ahead of schedule. 

Fish Passage

The dam caused an ecological blockade of aquatic life along the Wapsipinicon River, including the endangered Higgins eye mussel. Fish and mussels may move along the Wapsipinicon River with the newly created "fish ladders" on the west side of the river. The U.S. Fish and Wildlife Service recently stocked the river below the project site and at the Wakpicada Natural Area with over 3,000 smallmouth bass with glochidia (mussel) larvae attached for future growth. Additionally, over 21,000 walleye have been stocked by the Iowa DNR in this area during 2023.


Splash pools on the east side of the river enhances opportunities for anglers with additional fish habitat. Although this area is not a white water park, these new splash pools now allow for kayaks to venture downstream past the new river features. Paddlers may also choose to come to shore and down the walk to access the river past the features. All visitors should respect the river by continuing to keep safety in mind, observe safety signage, and proceed with any water activity with caution.

No-Rise Design

The project was designed in a way that would not result in higher water elevations upstream or downstream to cause a detrimental impact to Pinicon Ridge Park or the City of Central City. However, the park may still be prone to flooding from excessive rains and/or high river levels upstream, or lower water levels due to drought conditions.  Linn County Conservation and its engineering team's goal was to lower the dam while keeping adequate river pool depth upstream. 

WHKS & Co. was selected for engineering and design and Boomerang Construction of Anamosa was awarded the $3.4 million contract. The project is funded through Iowa Department of Natural Resources low-head dam/fish habitat, U.S Fish and Wildlife, and Linn County Water and Land Legacy Bonds.

2023 construction (timeline)

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Pinicon Ridge Park dam low-head dam dual function concept

The dual design addresses the goal of improving safety, fish passage, and recreational opportunities such as fishing and paddling.

Dam Modification site plan 

Additional Resources

Dam Safety

Numerous river rescues have taken place around the state at low-head dams (including two deaths over time at the Pinicon Ridge Park dam). These structures pose a risk to swimmers, boaters, and anglers, due in part to the recirculating current below the dam that can trap victims. Iowa Department of Natural Resources River Programs coordinator Nate Hoogeveen discusses the improvements to safety that dam modification projects create.

Dam Safety - Iowa Department of Natural Resources (Video)

Fish and Mussel Passage

The Wapsipinicon River is abundant in over 800 aquatic species, and the dam structure is currently an impediment to passage upstream. Data has been collected from successful migration patterns after other dam modification projects in eastern Iowa. Paul Sleeper, Fisheries Biologist for the Iowa Department of Natural Resources, explains the negative impacts a low-head dam has to aquatic life and the environmental health of the river.  

Fish Passage - Iowa Department of Natural Resources (Video)

Fish passage is critical for mussel passage along the Wapsipinicon River. Efforts continue to restore the mussel population, including the endangered species Higgins eye pearlymussel. Louise Mauldin, Fisheries Biologist from the U.S. Fish and Wildlife Service and her team, detail the importance of freshwater mussels. 

Mussel Community and Importance of Fish Passage at the Dam Site - U.S. Fish and Wildlife Service (Video)

The Reproductive Cycle and Importance of Freshwater Mussels - U.S. Fish and Wildlife Service (Video)