ST. LAWRENCE EASTERN LAKE ONTARIO PARTNERSHIP FOR REGIONAL INVASIVE SPECIES MANAGEMENT
DESCRIPTION:
Fanwort (Cabomba caroliniana) is a submerged invasive aquatic perennial plant native to South America, and the southeastern United States. It has become invasive in the northeastern US, as well as in Europe and Australia. Its name is derived from the fan-like appearance of its foliage.
DISTRIBUTION:
Fanwort spreads primarily through fragmentation. Fanwort has been found in the Hudson Basin, the Catskills, and Long Island. Fanwort has also been identified in Kasoag Lake in Oswego County. An infestation of fanwort was found in 2024 above the Youngs Mill Dam in Mexico, NY, in Oswego County. Fragments were found in Black Creek on the other side of the dam, and there is concern that it may spread into the Little Salmon River, which connects to Lake Ontario. A removal effort took place on August 29, 2024, in the vicinity of a reconstruction zone by the Dam and in areas with sparse populations of the plant downstream.
In the summer of 2025, SLELO PRISM, along with staff from the NYS DEC and the NYS Water Resources Institute at Cornell, conducted aquatic surveys on the Little Salmon River. They found that fanwort was primarily present at marinas on the River and think that it is primarily being spread by boats. Therefore, it is important that boaters inspect, clean, drain, and dry their watercraft before and after entering a waterbody.
IMPACTS:
Fanwort can overwinter and grow rapidly in the spring and summer, outcompeting and dominating native vegetation. Fanwort’s dense foliage reduces light availability for benthic organisms and native plants. This results in a decline in populations of fish and other animals dependent on these native organisms. Large diebacks of fanwort can result in reduced dissolved oxygen levels that can impact populations of aquatic species.
IF YOU FIND FANWORT:
Take a clear, close-up photo, note the location (GPS coordinates are best), and report observations to iMapInvasives or directly to the SLELO PRISM’s Aquatic Restoration and Resiliency Coordinator, Adrien Owens, Adrien.Owens@tnc.org.
We’re looking for volunteers to monitor rivers and streams that flow into Eastern Lake Ontario near New Hevan, Texas, Mexico, Pulaski, and Port Ontario, NY (below is a map with some suggested waterbodies to survey). If you own property on or frequent these or other waterbodies in the target region and would like to help keep an eye out for fanwort, please reach out to megan.pistolese@tnc.org.
Join early detection efforts for fanwort and other aquatic invasive species through our Water Protector’s Program. Participants will learn to recognize and report priority species to NYiMapInvasives and adopt a waterbody to monitor annually.
We host an Aquatic Invasive Species Learning Experience (AISLE) for Water Protector’s annually. This is a three part training held May-July that includes: a virtual plant identification session, a hands-on workshop, and a guided paddle.
Fanwort gets its common name from its submerged leaves that have a fan-like appearance and are arranged oppositely along the stem attached to a long petiole.
Submerged leaflets are finely divided and split like the letter “Y” at their tips.
Floating leaves are not as common as the submerged, but are often present when fanwort is in bloom and are narrow and diamond-shaped.
Flowers have six white petals with yellow stamens that bloom in June and July.
Fanwort can be confused with a few native aquatic plants. Water marigold, spiny hornwort, and coontail all have branching leaves that look similar to fanwort.
You can distinguish fanwort from these native lookalikes by checking for these characteristics: the presence of a long petiole, submerged leaves that are arranged oppositely along the stem in pairs, occasional floating leaves while flowering, white flowers June-July, and roots.
Fanwort can be controlled using chemical treatment, mechanical and manual harvesting, water level manipulation, and benthic barriers. However, these methods have had limited success or have ecological costs.
Fanwort is easily spread by plant fragmentation. Be sure to Clean, Drain, Dry your watercraft and equipment, and avoid driving watercraft through established fanwort colonies.