This submerged, rooted plant is native to the southeastern United States, but can now be found in many northeastern and northwestern states. Stems that can be up to six feet long are covered in fan-like leaves, and small, white, six-petaled flowers appear on the surface of the ponds, lakes and slow-moving streams that this aquatic weed inhabits in late summer. Fanwort spreads vegetatively (through broken stems), and by seed, and can be carried by moving water or from different bodies of water by pieces attached to boating equipment. In addition, although its sale is outlawed in several states, it remains a popular plant for aquariums, and is consequently sometimes dumped into new water bodies.
Fanwort changes the habitat for fish and other aquatic species, interferes with recreational use of the water body, changes oxygen levels and pH, and increases the organic content of the water body.
Prevention is easier than eradication, but if an infestation is discovered early enough, fanwort can be removed through hand harvesting and harvesting using a suction apparatus. This method reduces spread by fragmentation. Benthic barriers are effective, but they also kill all other vegetation in the affected area. Water level draw-downs and use of pesticides can also be effective control methods. Native alternatives include coontail and water marigold.