ZEBRA MUSSEL CONTROL EFFORTS ON THE ST. CROIX NATIONAL SCENIC
RIVERWAY MINNESOTA AND WISCONSIN.

Byron N. Karns.  
National Park Service, St. Croix National Scenic Riverway, St. Croix Falls, WI 54024.

In 1992, zebra mussels were discovered in the Mississippi River as it flows through Minneapolis. 
Downstream lies the St. Croix National Scenic Riverway, a unit of the National Park System.
Renown for its recreational and biological resources, the St. Croix River is nationally significant
for its richness and abundance of freshwater mussels (~40 species).  With the greatest diversity of
unionids in the Upper Mississippi watershed, the Riverway will be severely impacted by a zebra
mussel infestation.
Since that discovery of zebra mussels on the Mississippi River, the National Park Service has led
an interagency task force (U.S. Fish and Wildlife Service, Minnesota/Wisconsin Departments of
Natural Resources, MN/WI Boundary Area Commission, Minnesota Sea Grant, Great Lakes
Indian Fish and Wildlife Commission, St. Croix Marina Association, and others) designed to halt
or slow the spread of zebra mussels (Dreissena polymorpha) into the St. Croix Riverway. The
prevention efforts include education and information, access management, monitoring, planning
for remediation and research. A new element for the task force this year has been the formation
of an agency-staffed SCUBA dive team to monitor the river from under the surface.  With the
creation of a dive team staffed with members of the National Park Service and the Fish and
Wildlife Service, the river can be surveyed by trained biologists and experts, all of whom sit on
the task force.  Thus, monitoring conclusions and recommendations can be made with a unique
degree of first-hand information. The creation of a St. Croix dive team could not have come at a
more critical time in the history of the zebra mussels on the Riverway.  Zebra mussels have been
found attached to a small number of boats in the St. Croix since 1995 and individual mussels
have been discovered scattered in small numbers on substrate along the lower 25 miles of river. 
While these animals have had an individual presence on the river for a number of years, a
reproducing population has never been discovered in the St. Croix River.  Unfortunately, that
changed during the summer of 2000. This year, for the first time, zebra mussel reproduction has
been located within the lower 16 miles (or so) of the river.  The source of reproduction has yet to
be pinpointed, but the resulting settlement of juvenile mussels is very disturbing, if not
unexpected.  Armed with the unfortunate knowledge that the mussels have arrived, the task force
is beginning the painful chore of creating recommendations for policy makers and agency
managers.  The river may indeed be at a juncture in its ecological history.  What actions are taken
may be critical to the plants and animals that call the river home and a recreating public that
enjoys the many wonderful aspects of this nationally protected waterway.  The management
issues surrounding zebra mussels are complex and may be controversial.  This presentation will
focus on the multi-agency actions designed for 2001 and beyond.

Keywords: zebra mussel, St Croix River, interagency task force, monitoring