Eurasian watermilfoil is native to Europe, Asia and Africa. It may have arrived in the early 1900s through shipping or may have become established from plants that were originally contained in an aquarium.

Eurasian watermilfoil stems with leaves

Expansive mat of Eurasian watermilfoil on lake
Photo credit: A Fox/Univ. of Florida (left)
RL Johnson/Cornell Univ. (right)
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Reference
Southeast Exotic Pest Plant Council. http://www.se-eppc.org/.