Erected by St. Croix Scenic Riverway,
National Park Service, U.S. Department of the Interior
Shafer, Chisago County, Minnesota
A Refuge for Mussels
Mussels Need FishThe St. Croix River hides some of its most amazing features beneath its waters. This includes North America's most threatened animal -- the mussel.Why get excited about creatures that basically resemble rocks? Mussels are very long-lived animals sensitive to change in habitat and water quality, warning if the health of a river system begins to deteriorate. They also help keep rivers clean by filtering the water. Shells provide spawning and hiding habitat for fish and insects.The St. Croix boasts 40 species of native freshwater mussels -- more than any other river outside the southeastern United States. The river's clean water, forested land, and diverse environments help all mussels thrive.
Adult mussels use lure-like apendages to release glochidia (juvenile mussels) onto host fish. Glochidia spend their first few months attached to the fish's gills or fins, using nutrients from the fish in order to develop internal organs.Please protect mussels by leaving them and their shells in place.