Great Rivers Partnership - UMR - Wisconsin and Minnesota

The Upper Mississippi River Program

Lower St. Croix River: A River at Risk

The St. Croix River rises in northwestern Wisconsin and stretches for approximately 165 miles to join the Mississippi River about 20 miles southeast of the Minneapolis-St. Paul metropolitan area in Minnesota. Its 52-mile lower section begins at a hydroelectric dam at St. Croix Falls and runs between the two states.

While the river’s upper section runs through sparsely developed territory, the Lower St. Croix lies on the edge of the Minneapolis-St. Paul area. Water levels within the lower section are dependent on releases through the hydroelectric dam, which helps meet the metropolitan area’s need for electricity. While the Lower St. Croix remains scenic, environmental stresses upon its riverine ecosystem are already in evidence and are expected to increase.

The Lower St Croix is rich in aquatic species – in fact, it is one of most biologically diverse rivers in the Upper Mississippi River basin. At present, it shelters at least 40 mussel species, including the endangered winged mapleleaf and Higgins' eye mussels.
Recent studies, though, have indicated changes within the river are likely affecting the health of mussel communities. Non-native zebra mussels have invaded the Lower St. Croix and are competing with native mussels. Excess phosphorus levels are contributing to an increase in the growth of algae, which can adversely impact riverine habitat. The Minnesota Pollution Control Agency has classified the St. Croix as an impaired waterway for mercury and for polychlorinated biphenyls (PCBs).

The river’s watershed includes portions of two ecoregions – Superior Mixed Forest and Prairie Forest Border – and the terrestrial habitats found there also harbor significant biodiversity.

The human population within the St. Croix basin could increase by almost 40 percent by 2020, according to state and federal estimates. Foreseeing dramatically increased stresses on the river from such growth, public agencies, non-profit groups, scientists and other concerned parties in both of the river’s border states have stepped up their efforts related to the health of the St. Croix.

For example, the states of Minnesota and Wisconsin have agreed to cooperate in an effort to cut phosphorous levels in the St. Croix through such means as developing nutrient management plans for farms and installing filtration basins to intercept urban runoff. The Wisconsin Department of Natural Resources and the company that operates the St. Croix Falls hydroelectric dam have signed an agreement under which the dam will be operated for three years to mimic natural water flow conditions, a test to determine whether such a change would benefit aquatic life downstream.

The Nature Conservancy, in part through its Minnesota chapter’s membership in the Minnesota Environmental Partnership, already has been working to ensure a better future for the St. Croix. Now, the Conservancy’s Upper Mississippi River Program has selected the Lower St. Croix as a priority conservation site and is currently assessing the river’s conditions and environmental stresses to determine ways to further conservation of the St. Croix and the plants and animals that depend on it.

The Conservancy’s Upper Mississippi River Program, Lower Mississippi River Program and Great Rivers Partnership seek to advance the Conservancy’s national and global efforts to protect the Earth’s critically important freshwater resources for the benefit of the people and other living things that depend upon them for life.

Canoeist on the Saint Croix River

Canoeist on the Saint Croix River in Wisconsin's Interstate Park on the Wisconsin, Minnesota border northeast of Minneapolis, MN
© Mark Godfrey

UMR Program

Priority Sites