Eurasian Watermilfoil arrived in North America, most likely in ship ballast or as an aquarium plant, and proceeded to spread into nearly every state and much of Canada. Native to Asia, Europe, and Africa, Myriophyllum spicatum grows in water three to thirteen feet deep with stems reaching twenty feet, the feathery whorled leaves reducing drag and the plant thriving in cold, low-light conditions that defeat many competitors. In summer it pushes a two- to six-inch spike of tiny reddish or pinkish flowers above the surface, but reproduction is primarily vegetative — each stem fragment is a potential new colony, and one disturbed plant can scatter hundreds of viable pieces.

The ecological toll is substantial. Dense mats displace native aquatic plants and alter the habitat structure that fish and waterbirds depend on. The plant clogs hydropower turbines, obstructs navigation, and can hybridize with native watermilfoil species — including Myriophyllum sibiricum — producing fertile hybrids that are harder to control than either parent. It is on the NC noxious weed list, considered invasive by the NC Invasive Plant Council, and illegal to sell in many states. Mechanical removal is largely counterproductive without follow-up treatment, as fragmentation speeds spread. This entry is included here for identification purposes.