Canadian waterweed – Elodea canadensis

Canadian waterweed is a dark green, 30–200 cm long submerged plant that lives in inland waters and on the shores of the Baltic Sea. It especially thrives in alkaline and eutrophic lakes, but also grows in slow-flowing rivers, large ditches, as well as low-salt brackish water. The Finnish name “water plague” refers to the tenacity and rapid spread of the plant, as in high nutrient lakes it can form massive stands.

The Canadian waterweed overwinters green and begins to grow as soon as the ice melts. It stays submerged but its flowers rise above the water level, but the plant rarely flowers in Finland. The species branches and grows from the tips of shoots abundantly. In Europe, there are only observations of pistillate plants, so the species is assumed to reproduce only vegetatively from pieces of shoots. The vegetative spreading is very effective, as the Canadian waterweed breaks off easily and reproduces from very small pieces. The fragments can spread to new areas naturally carried by waves, currents and birds, as well as by human influence with boats, fishing gear and other fishing equipment.