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Zebra mussels found in Crystal Lake

  • 6/25/2019 12:49:00 PM
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The Iowa Department of Natural Resources (DNR) is closely monitoring Crystal Lake for zebra mussels after recent discoveries of juveniles in a water sample and two individuals on a sampling plate used to monitor for zebra mussels. No adult zebra mussels were found during a follow-up survey.

The DNR collects water samples and deploys settlement samplers in lakes across Iowa each summer to monitor for the invasive zebra mussel. DNR staff will collect water samples monthly in Crystal Lake this summer, and will survey hard substrate later this summer and fall to determine if Crystal Lake has an established population of zebra mussels.

“Finding zebra mussel veligers and a couple individuals at the boat ramp shows us that zebra mussels have been introduced into Crystal Lake,” said Kim Bogenschutz, the DNR’s Aquatic Invasive Species Program coordinator. “It’s still too early to tell though if there is an established population in the lake.”

The presence of zebra mussels in another lake highlights the spread of aquatic invasive species in Iowa waters. “The zebra mussels in Crystal Lake probably arrived on or in a boat that had picked up the mussels from an infested water body, like nearby Clear Lake,” said Bogenschutz.

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, ballast or bait buckets.  Adult zebra mussels can attach to boats, trailers and aquatic vegetation.

Zebra mussels are filter feeders that can form dense clusters as they attach to hard underwater surfaces.  Large infestations may interfere with aquatic food chains, kill native mussels, clog water intakes, increase algae blooms, and cover beaches with dead shells.  Currently, there is no effective treatment to control zebra mussels once they have infested a lake. 

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 they leave a water access and must keep drain plugs removed or opened during transport.

“Boaters and anglers can unintentionally spread zebra mussels and other aquatic invasive species if they do not take the proper precautions - clean, drain, dry - after each time out on the water,” said Bogenschutz.

  • CLEAN any plants, animals or mud from boat and equipment before you leave a water body.
  • DRAIN water from all equipment (motor, live well, bilge, transom well, ballast bags, bait bucket) before you leave a water body.
  • DRY anything that comes into contact with water (boats, trailers, equipment, boots, clothing, dogs). Before moving to another waterbody either:

Spray your boat and trailer with hot, high-pressure water; or

Dry your boat and equipment for at least five days.

  • Never release plants, fish or animals into a water body unless they came out of that water body and empty unwanted bait in the trash.

“Draining all water is a critical step in preventing the spread of zebra mussels,” said Bogenschutz.

Find more information about aquatic invasive species and a list of infested waters in the 2019 Iowa Fishing Regulations or on the DNR’s website at

If you see a zebra mussel, please note its location and contact your local fisheries office or the Aquatic Invasive Species Program in Boone.