Coreyon: Restoring Fish Spawning Habitat (DRAFT PAGE)

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

[add details from initial assessment reports?]


  • 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


Possible photos LINK to DRIVE: Fish over a reef, Detroit River diagram modified with season (fall, next to walleye and remove sturgeon)


  • 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 EPA’s Great Lakes Restoration Initiative.
  • 2016: The Coreyon site was identified as a priority for rock reef restoration.
    [partners need to confirm timeline from here]
  • 2019: Construction began on Coreyon reef.
  • 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. [add graphic]
  • 2019-Present: Researchers monitor conditions at the reef to assess fish spawning activity.


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

A. 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. 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 mimics them by using limestone cobble (e.g. fieldstones) of about 8 inches in diameter. 10,000 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 2 to 4 feet from the lake bottom. The height of the rock pile varies 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 the Michigan DNR and its partners at Purdue University have documented walleye and lake whitefish spawning there.

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, and Saginaw Bay Watershed Initiative Network, Michigan DNR and Michigan EGLE. The total reef construction project cost $1,185,000.

Supporting Fish Habitat in Saginaw Bay (PDF)