sentences:  Recently, "E. densa" was reported as naturalized alien species in Iceland where it invaded the naturally heated water bodies.Due to its occurrence in northern Iceland, "E. densa" is one of the first freshwater alien plant species that reached the Arctic.Most of its impact occurs in the shallow waterways; the plant forms thick mats that obstruct boat passage, clog water intakes and aqueducts, trap sediments, crowd out native vegetation, and impede the migration of anadromous fish.