WEST OKOBOJI — State environmental officials moved quickly after discovering a small population of a highly invasive aquatic plant growing in a canal connected to one of Northern Iowa’s most popular recreational lakes.
The Iowa Department of Natural Resources and staff from the Iowa Lakeside Laboratory recently found Eurasian watermilfoil in the canal system south of Miller’s Bay at West Okoboji Lake (pictured at top).
Officials said the infestation was small and isolated. No Eurasian watermilfoil was discovered in the main body of West Okoboji Lake or any of the other lakes in the Iowa Great Lakes chain.
“After the discovery of Eurasian watermilfoil deep in the West Okoboji Lake canals, we acted swiftly to control the plant using an effective, safe, milfoil-focused herbicide treatment,” Iowa DNR fisheries biologist Andrew Carlson said.
Carlson said permits were already in place, allowing crews to respond rapidly and begin controlling the invasive plant before it could spread farther.
“We are thankful for community funding and staff at the Iowa Lakeside Laboratory for helping isolate the plants,” Carlson said.
Eurasian watermilfoil is a rooted aquatic plant native to portions of Europe and Asia. It can grow rapidly, crowd out beneficial native vegetation and form thick underwater beds capable of disrupting boating, fishing and other recreational activities.
The plant can spread through fragmentation, meaning even small pieces cut or broken away from an established plant can produce new growth elsewhere.
The latest discovery comes as the DNR continues battling the invasive plant in other parts of the state. NIT previously reported that Eurasian watermilfoil had spread into portions of Clear Lake, prompting additional management and treatment efforts.
Iowa’s Aquatic Invasive Species Program has worked for more than 30 years to control Eurasian watermilfoil and prevent it from spreading into additional lakes. The DNR’s Aquatic Plant Management team surveys vegetation throughout the Iowa Great Lakes each year.
Officials are asking boaters, anglers and other lake users to be especially careful when traveling through the affected canals and moving between different bodies of water.
The DNR recommends that boaters follow its Clean, Drain, Dry procedure every time watercraft or equipment is moved.
CLEAN all plants, animals and mud from boats, trailers and equipment before leaving a body of water. Boaters using the affected canal system should carefully inspect propellers and other areas where pieces of vegetation could become trapped before entering the main lake.
DRAIN all water from motors, live wells, bilges, transom wells, bait buckets and other equipment before leaving the water access.
DRY boats, trailers, equipment, boots, clothing and anything else that came into contact with the water. Equipment should be sprayed with hot, high-pressure water or allowed to dry for at least five days before entering another body of water.
Unwanted bait should be placed in the trash. Plants, fish and other animals should never be released into a body of water unless they originally came from that same water.
It is illegal in Iowa to possess or transport prohibited aquatic invasive species, including Eurasian watermilfoil. Boaters are also required to drain water from their boats and equipment before leaving an access area and must keep drain plugs removed or open during transport.
More information about aquatic invasive species and infested Iowa waters is available through the 2026 Iowa Fishing Regulations booklet and the Iowa DNR.