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Zebra mussels found in Lake Manawa

  • 7/21/2020 12:55:00 PM
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The Iowa Department of Natural Resources (DNR) recently confirmed that zebra mussels are in Lake Manawa.

A homeowner on Lake Manawa reported finding zebra mussels on rip-rap along his shoreline. Investigation by DNR staff discovered low numbers of zebra mussels around the lake. DNR staff will conduct additional surveys at Lake Manawa this fall and next summer to monitor the abundance and distribution of zebra mussels.

The documentation of zebra mussels in another lake highlights the spread of aquatic invasive species in Iowa waters. “The zebra mussels in Lake Manawa probably arrived on or in a boat that had picked up the mussels from an infested water body, like the nearby Missouri River,” said Kim Bogenschutz, DNR Aquatic Invasive Species Program coordinator.

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.  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. 

Young zebra mussels are microscopic and can be unintentionally transported with water in live wells, bilges, ballast 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 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 to clean, drain, and 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, bait bucket) before you leave a water body.
  • DRY anything that comes into contact with water (boats, trailers, equipment, boots, clothing, dogs). Before you move to another waterbody either:
  • Spray your boat and trailer with hot, high-pressure water; or
  • Dry your boat and equipment for at least 5 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,” reminds Bogenschutz.

Find more information about aquatic invasive species and a list of infested waters in the 2020 Iowa Fishing Regulations booklet or on the DNR’s website at