Spirit Lake – As docks and hoists are being removed from most of Iowa’s Great Lakes, a most unwelcome visitor is being discovered in greater numbers.

Zebra mussels, first discovered in East Okoboji Lake and Upper Gar Lake in the fall of 2012, have been increasing in numbers and distribution the past few years throughout most of the Iowa Great Lakes. Spirit Lake is the only lake where adult zebra mussels have not been found.

This fall, the number of zebra mussels on docks and hoists removed from East Okoboji has noticeably increased. Residents who observe zebra mussels on docks and hoists removed from Spirit Lake are requested to report the location to the DNR Fisheries office in Spirit Lake.

Zebra mussels look like small, D-shaped clams that have alternating light and dark bands. Most are less than one-inch long. Young zebra mussels are microscopic and can be unintentionally transported with water in bilges, live wells or bait buckets.  Adult zebra mussels can attach to boats, trailers and aquatic vegetation.

It is illegal to possess or transport zebra mussels and other prohibited aquatic invasive species in Iowa. It is also illegal to transport any aquatic plants on water-related equipment. Boaters must drain all water from boats and equipment before leaving a water access and must keep drain plugs removed or opened during transport.

The DNR is working with Iowa Great Lakes service providers to help prevent the introduction of zebra mussels or other aquatic invasive species to additional waters. Providers will be provided a permit to transport water-related equipment that is or may be infested with zebra mussels and aquatic plants to an approved storage location via an approved route. All equipment removed must be allowed to dry a minimum of 10 days and all mussels and plant materials must be removed before being moved outside of the approved area.

The impact to the Iowa Great Lakes is unclear as zebra mussels become established. Zebra mussels are filter feeders and directly compete with native species, including mussels and small fish, for food. Zebra mussels also adhere to hard objects. If densities are high enough, they can smother native mussels by attaching to their shells. Drinking water utilities and the State Fish Hatchery are also impacted since zebra mussels could attach and grow on the inside of intake pipes, potentially clogging them.

The Iowa Great Lakes community has provided important leadership to the state of Iowa in fighting aquatic invasive species.

“This strong partnership and the continuation of these efforts remains our best weapon against these invaders,” said Mike Hawkins, Spirit Lake District fisheries management biologist.