Canadian waterweed – Elodea canadensis

Canadian waterweed is originally native to North America. It spread to Europe in 1836, and a specimen was brought to the University of Helsinki botanical gardens in 1884. However, the species has probably entered Finland on multiple occasions. It particularly thrives in alkaline, high-nutrient shallow lakes and bays, and in slowly flowing rivers and ditches. Fragments of Canadian waterweed shoots may float and travel along waves, currents, boats, ships, fishing gear or with waterfowl from one water body to another.

Today, Canadian waterweed is established in southern Finland and the southern parts of central Finland. Also, it is spreading aggressively in the Koillismaa region in the northeast Finland. Furthermore, individual occurrences can be found here and there, e.g. in brackish waters along the Finnish coast.