July 25, 2006
The Iowa Department of Natural Resources (DNR) has confirmed the
presence of zebra mussels in Lake Delhi, an on stream impoundment of
the Maquoketa River, in Delaware County. Local residents recently
contacted the DNR after discovering zebra mussels attached to
concrete block they removed from the lake. Further investigation
revealed additional mussels on rocks above and below the dam.
"The number and various sizes of zebra mussels that were found
appear to indicate that there is a reproducing population in the
lake," said Kim Bogenschutz, the DNR's aquatic nuisance species
Zebra mussels look like small, fingernail-sized clams. The D-shaped
shells have alternating light and dark bands, and most are less than
one inch long. Zebra mussels are filter feeders that can form dense
clusters as they attach to hard underwater surfaces. In the case of
large infestations, they may interfere with aquatic food chains,
kill native mussels, clog water intakes, increase algae blooms, and
cover beaches with dead shells. There is no getting rid of zebra
mussels once they are in a lake or river.
Zebra mussels are native to the Caspian Sea region of Asia and were
introduced into the Great Lakes in the 1980s from ballast water of
oceangoing ships. They spread from the Great Lakes to the
Mississippi River and were first documented in the Mississippi River
in Iowa in 1992. There were no reports of zebra mussels in interior
waters until 2005 when two adults were found in Clear Lake and in
2006 when juvenile zebra mussels were reported from the same area in
DNR biologists plan to continue monitoring Lake Delhi to determine
the distribution of zebra mussels in the lake and in the Maquoketa
River below the dam.
One thing is certain, the sighting of zebra mussels in Lake Delhi
highlights the spread of invasive species in Iowa water, she said.
"The zebra mussels in Lake Delhi probably arrived on or in a boat
that had picked up the mussels in an infested water body," said
Young zebra mussels are microscopic and can be unintentionally
transported with water in live wells or bait buckets. Adult zebra
mussels can attach to boats, trailers, and aquatic vegetation. If
boaters come from an infested water body, they can unintentionally
transport zebra mussels, Eurasian watermilfoil, or other aquatic
invasive species if they do not take the proper precautions to
prevent their spread.
Bogenschutz emphasized that anglers and boaters can help prevent the
spread of aquatic invasive species by following the steps outlined
* Inspect your boat, trailer, and equipment and remove visible
aquatic plants, zebra mussels, other animals, and mud before leaving
a water access.
* Drain water from bait buckets, live well, bilge, transom, and
motor before leaving a water access.
* Dispose of unwanted live bait and worms in the trash. Never
release plants, fish, or animals into a water body unless they came
out of that water body.
* Spray/wash your boat, trailer, and equipment with high pressure or
hot water before going to other waters, OR
* Dry everything for at least five days before going to other
The DNR will work with local units of government and the lake
association to increase public awareness efforts to control the
further spread of zebra mussels. The DNR is also requesting the help
of anglers, boaters, and homeowners in the search for zebra mussels
in Lake Delhi. If you see a zebra mussel, please note its location
and contact Bryan Hayes, the local fisheries management biologist,