There are 41 species of native mussels in the St. Croix River as well as two species of introduced bivalves (zebra mussels and Asian clams).

There are five federally endangered species of mussels – the spectaclecase (Cumberlandia monodonta), the snuffbox (Epioblasma triquetra), the Higginsi Pearly Mussel (Lampsilis higginsii), the sheepnose (Plethobasus cyphyus), and the winged mapleleaf (Quadrula fragosa). In addition there are a number of species listed as endangered or threatened in the states of Minnesota and Wisconsin.

• Summary of the distribution of mussels in the St. Croix based on quantitative sampling completed by the Macalester team.
• Map of the St. Croix River that provides interactive access to more of the data on mussels in the river.
• List of species and their conservation status.

There have been a number of qualitative and quantitative studies of the mussel assemblages of the St. Croix River. Much of the information has been summarize in:

Hornbach, D.J. 2001. Macrohabitat factors influencing the distribution and abundance of naiads in the St. Croix River, MN and WI, USA, pp. 213-230. In G. Bauer and W. Wächtler [eds] Ecology and Evolutionary Biology of the Freshwater Mussels Unionoidea. Ecological Studies Vol. 145 Springer Verlag: Berlin.

In this paper Hornbach has examined the factors which may help to explain the distribution of mussel species in the river. More information.

In addition Hornbach and researchers at Macalester College have been conducting quantitative studies of populations at 9 sites on the St. Croix River. The methods used can be examined here.

The results of the quantitative studies have been published in:

Hornbach, D.J., D.C. Allen, M.C. Hove and K.R. MacGregor. 2018. Long-term decline of native freshwater mussel assemblages in a federally protected river. Freshwater Biology 63: 243-263 (DOI: 10.1111/fwb.13055)

In 2015 we sampled locations on the Snake River Wateshed of the St. Croix as part of our LCCMR project examining sediment impact on mussels of the Minnesota River Watershed. The Snake River is being used as a reference site. We revisited sites early surveyed by the MN DNR using a catch-per-unit-effort method (collecting all mussels within a specified time period.

The results of this work have been published in:

Hornbach, D.J., H.N. Stutzman*, H.N., M.C. Hove, J. L. Kozarek, K. R. MacGregor, T. J. Newton and P.R. Ries. 2019. Influence of surrounding land-use on mussel growth and glycogen levels in the St. Croix and Minnesota River Basins. Hydrobiologia,  doi/10.1007/s10750-019-04016-z

Hornbach, D.J., M.C. Hove, K.R. MacGregor, J.L. Kozarek, B.E. Sietman, and M. Davis. 2019. A comparison of freshwater mussel assemblages along a land use gradient in Minnesota. Aquatic Conservation: Marine and Freshwater Ecosystems 29:1826–1838. doi/ 10.1002/aqc.3167.