Fanwort (Cabomba caroliniana) is a hardy invasive plant that originates primarily from regions with warm, humid, subtropical climates such as those found in southeastern regions of North America and northeastern South America. It is a fully submerged aquatic plant with the exception of a white or pale yellow flower that floats on the water's surface.
Because of its high popularity as an aquarium plant, it has been cultivated in Asia and the south east of the United States for commercial use and has been dispersed in many parts of the world. Although it originates from regions with warm, temperate climates, it can survive in below-freezing temperatures. Today in North America it can be found in over 30 states and was first reported in southern Ontario in 1991.
Fanwort thrives best in stagnant and slow flowing environments such as lakes, small rivers, streams and ditches. It is a perennial plant that spreads via vegetative reproduction through stem fragments or rhizomes.
In the proper environment, fanwort grows rapidly and becomes a very persistent and competitive invader by producing large amounts of plant material that form dense stands and eventually overtake native aquatic plants, obstruct drainage canals and hinder aquatic recreational activities such as swimming and boating. Decomposition of this abundant plant material results in significant reductions in dissolved oxygen levels necessary for survival of fish and other organisms and causes foul odours in the water.
Fanwort can be easily spread by watercraft or other equipment, etc., that pick up stem fragments and disperse them to new locations, as well as by water currents. Because of its persistence and potential for spread, fanwort is very difficult to control. Various methods, including mechanical removal, reducing water levels by draining to dry out the plants (fanwort requires permanent shallow water to survive), shading of areas to reduce sunlight and application of chemical herbicides, have been used but either only provide temporary results or can only be employed under specific conditions.
Preventive measures remain the best means of controlling its spread. These measures include washing down of boats, watercraft and other aquatic equipment that circulate in infested areas, only draining aquarium water on dry land and not into natural waters, drainage ditches or sewers and, when possible, returning or donating unwanted aquarium plants to a pet store or school.
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