Eurasian watermilfoil confirmed in Big Mantrap Lake

July 13, 2020

The Minnesota Department of Natural Resources has confirmed Eurasian watermilfoil, an invasive aquatic plant, in Big Mantrap Lake near Emmaville in Hubbard County. Big Mantrap Lake is near Bad Axe Lake, where Eurasian watermilfoil was first confirmed in Hubbard County in 2017.

Big Mantrap Lake is a popular destination for anglers fishing for muskellunge, northern pike, largemouth bass, and panfish such as bluegill and crappie.

A small piece of Eurasian watermilfoil was found near the public access last fall, but nothing further was found at that time. After an extensive search last week, a DNR invasive species specialist found a small population of Eurasian watermilfoil near the public access. She removed all visible specimens by hand. The lake association is discussing potential follow-up treatments.

Treatment options include systemic herbicides, which can minimize the plant’s impact while protecting native aquatic plant species. Treatment is unlikely to eradicate Eurasian watermilfoil from a lake. It may minimize impacts but rarely prevents broader dispersal within a lake.

Eurasian watermilfoil can limit recreational activities on water bodies by forming mats on the water surface, and can alter aquatic ecosystems by displacing native plants. It is typically spread when plant fragments have not been properly cleaned from trailered boats, personal watercraft, docks, boat lifts, anchors or other water-related equipment. 

With this new confirmation, the DNR reminds boaters and anglers to follow Minnesota laws to prevent the spread of aquatic invasive species:

  • Clean aquatic plants and animals from boats, trailers and equipment.
  • Drain all water by removing drain plugs, and keep drain plugs out while transporting watercraft.
  • Dispose of unwanted bait in the trash.

Some invasive species are small and difficult to see at the access. To remove or kill them, take one or more of the following precautions before moving to another waterbody, especially after leaving infested waters:   

  • Spray with high-pressure water.
  • Rinse with very hot water (120 degrees for at least two minutes or 140 degrees for at least 10 seconds).
  • Dry for at least 5 days.

Details about Eurasian watermilfoil and other aquatic invasive species are available at