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North Dakota Species of Conservation Priority I

Fact Sheet
Scientific Name Potamilus ohiensis
General Description Large mussel with a maximum length of 7 inches. Shell is elongated and generally rectangular. Wing present near the umbos. Shell dark green to brown. Nacre is pink.
Status Year-round resident.
Abundance Locally common.
Primary Habitat Prefer large rivers with a mud, sand or gravel substrate. In North Dakota confined to larger rivers.
Federal Status None.
Reason for Designation Believed to be declining in state waters. Changes in land use in and around these rivers, most notably agriculture, and impoundment of river systems, may impact mussel populations. They are also of commercial value and are protected from harvest in North Dakota.



(Photos courtesy of Prairie Waters Education and Research Center - Valley City University)

Locations and Conditions of Key Habitat

Preferred Habitat

Threeridge prefer large river systems. The substrate of the river is normally mud, sand, or gravel.

Key Areas and Conditions for Threeridge in North Dakota

Found only in the Red and Sheyenne rivers. It is found in highest concentrations in the section of the Sheyenne River in Ransom County.

Problems Which May Affect this Species


Impoundment of the Red River and its tributaries have changed the flow regime and increased sediment deposits making many areas in the river unsuitable to the Creek Heelsplitter. Impoundments also block host fish movement necessary for this species’ reproduction and dispersal. Agricultural practices within the basin have reduced suitable habitat in the river. Runoff from treated fields into the river decreases water quality. Ditches used to drain wetlands contribute agricultural run-off and sedimentation to the Red River and its tributaries.

Other Natural or Manmade Factors

The Threeridge is considered a commercially valuable species. It is presently illegal to collect mussels for commercial use in North Dakota, but this practice may occur in parts of its range. This may contribute to an already declining population. The release of water from Devils Lake changing the water chemistry of the Sheyenne River is a potential threat.

Research and Survey Efforts

Current Research or Surveys

  • No current research or survey efforts are on-going in this species range.

Previous Research or Surveys

  • Cvancara conducted a state-wide survey of the mussels of North Dakota in 1978.
  • The North Dakota Game and Fish Department revisited Cvancara’s sites in 1990.
  • Valley City State University revisited Cvancara’s sites and surveyed additional sites in 2008.
  • The NDDH conducted freshwater mussel surveys for state waters as a segment of its Index of Biotic Integrity (IBI) work.

Additional Research or Surveys Needed

  • A monitoring protocol for mussel species has been developed for the North Dakota Game and Fish Department under the SWG program. Implementation of this monitoring protocol is a future goal.

Management Recommendations

  • Develop buffers along riparian areas.
  • Work with partners to reduce the use of chemical near waterways.
  • Work with partners to reduce wetland drainage.
  • Remove river impoundments where possible.
  • Work with partners to maintain instream flows.

Monitoring Plans

A monitoring protocol has been developed for the North Dakota Game and Fish Department under the SWG program. Implementation of this monitoring protocol is a future goal.

2005-2015 Progress

SWG T-24-R A Two Phase Population Survey of Mussels in North Dakota Rivers provided important information on the distribution of this species. Work to implement a monitoring protocol for mussels species will is a goal of the revised Wildlife Action Plan.

Range Map

Note: A listing of works consulted when compiling the information on this page may be found in the 2015 State Wildlife Action Plan.