The Iowa DNR is watching Big Spirit Lake after a resident found a single juvenile zebra mussel attached to a rock in the southwest side of the lake on Sept. 23.
Biologists at the DNR’s Boone research facility also found a single larval zebra mussel in a water sample collected from Big Spirit Lake in August. The DNR collects water samples and deploys settlement samplers in lakes across the state each summer to monitor for the invasive zebra mussel.
The first zebra mussels in the Iowa Great Lake chain were discovered in the fall of 2012 and have increased in numbers since. Big Spirit Lake flows over a spillway into the rest of the Okoboji Chain.
“Finding both a zebra mussel veliger and juvenile indicates to us that zebra mussels have been introduced into Big Spirit Lake,” said Kim Bogenschutz, the DNR’s Aquatic Invasive Species Program coordinator. “It’s too early to tell if there is an established population in the lake, but it is likely since the other lakes in the chain have growing populations.”
Zebra mussels look like small, D-shaped clams that have alternating light and dark bands. Most are less than one inch long. They 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.
The City of Spirit Lake recently completed upgrades to their drinking water intakes in the lake in preparation for a possible infestation.
Biologists will inspect boat hoists and docks after they come out this fall for storage.
“These structures are quickly colonized and are good indicators of how prevalent mussels are in the lake,” said Mike Hawkins, Spirit Lake District fisheries management biologist.
The Spirit Lake Fish Hatchery uses raw water from Big Spirit Lake in the production facility. Zebra mussels can be filtered and killed in the water used to haul fish from the hatchery to other water bodies. The Spirit Lake Fish Hatchery, along with other Iowa hatcheries, has implemented plans for many years to prevent the spread of zebra mussels and other aquatic invasive species when stocking fish.
“Although we can treat the water leaving the hatchery, zebra mussels can clog pipes and valves, making the infrastructure at the Spirit Lake Hatchery vulnerable to the infestation,” said Hawkins. “Important upgrades are needed to protect the facility.”
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 prohibited aquatic invasive species, such as zebra mussels, in Iowa. Boaters must also drain all water from boats and equipment before leaving a water access and must keep drain plugs removed or opened during transport.
More information about aquatic invasive species and a list of infested waters can be found in the Iowa Fishing Regulations booklet. If you find a zebra mussel, note its location and contact your local fisheries office or the Aquatic Invasive Species Program in Boone.