Coreyon: Restoring Fish Spawning Habitat

Site: Off-shore in Inner Saginaw Bay, about 8.5 miles west of Fish Point or 10 miles north of Quanicassee (coordinates: 43° 44’ 3.704” by -83° 41’ 5.173”)

Project: 2-acre rocky fish spawning reef

  • Primary focus: Spawning habitat for native fish species like walleye and lake whitefish
  • Secondary focus: Generate data and best practices for future reef restoration projects

Project status: Completed

Why here?

Healthy fish populations and diverse habitats are key to a strong, resilient Saginaw Bay.

Map of Saginaw bay with Coreyon reef location


  • Diversify habitat, especially spawning habitat, for native fish species
  • Improve recreational and commercial fishing opportunities
  • Ensure safe navigation and access for boat traffic
  • Create demonstration site for future restoration projects


  • 2004: Michigan DNR published a Walleye Recovery Plan that included calls for the restoration of some off-shore rock reef spawning habitat to help diversify sources of reproduction.
  • 2008-2013: NOAA led an assessment of environmental stressors in Saginaw Bay. The study indicated that sedimentation rates had decreased in some nearshore habitats.
  • 2014-2016: Federal, state, local, and academic partners assessed physical and biological conditions of several historical reefs, which had been blanketed by sediment. Results showed that only remnants of the reefs remained, not enough to support spawning by recovering populations of lake whitefish and walleye. The assessment also identified potential reef restoration sites. Assessment funding came from the Great Lakes Restoration Initiative.
  • 2016: Selection of the Coreyon site was finalized.  
  • July 2019: Construction began on Coreyon reef.
  • September 2019: Construction was completed on Coreyon reef.
  • 2020: Coreyon documentary told the story of this important restoration project.
  • 2020: Informational signs about the project were installed at public boat launches. The signs were developed with assistance from Bay Western Middle School students.
  • 2019-present: Researchers with Michigan DNR, EGLE, and Purdue University monitored conditions at the reef to assess fish spawning activity.


Why was it important to add this spawning reef to Saginaw Bay?

Due to factors like invasive species, habitat loss, and poor water quality, Saginaw Bay’s prized walleye fishery collapsed in the 1940s. Since then, regulation and partnerships have helped restore Saginaw Bay. Today, the walleye fishery has recovered. However, this important fishery is now largely sustained by fish spawned in the Tittabawasse and Kawkawlin rivers. This has created a fishery dependent on a limited source of natural reproduction, leaving it vulnerable to external stressors and population instability. In addition to walleye, other important species such as lake whitefish also seek out and spawn on off-shore rock reef habitat. Having diverse spawning locations helps restore historical conditions and makes fish populations more resilient in the face of environmental stressors. 

What is the reef made of?

Historically, rock reefs formed in the Great Lakes as glacial deposits. Coreyon reef was designed to experiment with two types of rock: glacial cobble and limestone cobble about 8 inches in diameter. The surface of the reef was split between the two types so researchers could monitor any differences in fish spawning activity. 16,000 cubic yards of rock (22,500 tons) were placed on the lakebed by barge and crane. This created a pile of rocks covering 2 acres and rising an average of 5 feet from the lake bottom. The height of the reef was designed to prevent navigational hazards and maintain a minimum of 6.5 feet of water depth based on the recorded low water level.

Is the reef working?

Yes, research performed by Michigan DNR and its partners at Purdue University have documented walleye and lake whitefish spawning there. Initial results don’t show fish selecting one type of cobble more than the other.

Who paid for this project?

Different grants supported each step of the assessment, design, and construction process. Primary funding sources included the U.S. Environmental Protection Agency, Great Lakes Restoration Initiative, Saginaw Bay Watershed Initiative Network, Michigan DNR, and Michigan EGLE. The total reef construction project cost $1,185,000.

Who worked on this project?

The project was principally overseen by Michigan DNR and EGLE. Much of the early engineering and day-to-day project oversight was performed by ECT Inc, a nongovernmental consulting company. Various suppliers and contractors did the actual rock placement. Other partners included federal agencies, Michigan Sea Grant, and Bay County.