The alarming expansion of a northern hydrilla subspecies outside the Connecticut River is raising significant concerns. This aggressive aquatic weed, considered among the “world’s worst,” is now present in five additional Connecticut water bodies and one in Massachusetts, according to recent findings published in Invasive Plant Science and Management.
Jeremiah Foley, an assistant agricultural scientist at the Connecticut Agricultural Experiment Station and lead author of the study, expresses grave concern about the recent spread and establishment of another hydrilla subspecies in the U.S., highlighting the significant negative impact this invasive aquatic weed can have on native aquatic and terrestrial plant and animal species given how rapidly it is spreading.
Until 2022, this subspecies had only been identified in the Connecticut River. However, by the end of 2023, researchers found it in five additional water bodies in Connecticut and one in Massachusetts. Foley notes that managing the two previously established hydrilla subspecies, which have been present since the 1960s and 1980s, already requires significant resources. The discovery of Hydrilla verticillata subspecies lithuanica in the Connecticut River and its current widespread infestation signals a considerable ecological invasion with potentially important consequences.
Nearly all the newly infested locations were found close to boat-launch ramps. Foley points out that East Twin Lakes, Amos Lake, and Congamond Lakes regularly host angling tournaments that draw participants statewide. Traveling from infested to non-infested waters is particularly concerning, underscoring the need for stricter controls to limit the spread. As hydrilla can displace native aquatic plants and serve as a host for a bacterium that produces neurotoxins linked to the deaths of bald eagles and waterfowl, Foley recommends bolstering education for boaters and monitoring tournament impacts to prevent further propagation. The primary mode of hydrilla’s introduction to new water bodies is through boats and trailers. To combat this, Foley suggests thoroughly cleaning boating equipment and avoiding using the weed in home aquariums.
Native to India and Korea, hydrilla was introduced to Florida in the early 1950s as an aquarium plant and now thrives in water bodies up to 25 feet deep. Its dense mats impede boating, fishing, and swimming, and it can alter water chemistry and dissolve oxygen levels, causing further ecological damage. Managing the invasive plant costs Florida millions annually, and the U.S. Department of Agriculture lists the species as prohibited. Mechanical harvesters, manual removal, and lake drawdowns can help manage smaller infestations, though fragmented hydrilla that are not collected can further propagate the weed. Biological controls have limited success, with only one insect proving consistently effective.
