Wicked water weed causes ‘significant ecological invasion’

This is the first of a series on invasive aquatic hydrilla and its growing threat to waterbodies and communities in Northwest Connecticut.

SALISBURY — It was only a matter of time.

Since 2016, an aggressive non-native aquatic plant, Hydrilla verticillata, also known as water thyme, has fouled coves and tributaries along the Connecticut River from Essex to the Massachusetts border, leaving unprecedented ecological, recreational and economic damage in its wake.

Now it has hitched a ride via unsuspecting boat owners to inland freshwater lakes and ponds around the state, causing concern among lake associations, town and state officials.

To date, the submerged perennial plant, fittingly named after Hydra, the nine-headed serpent from Greek mythology known for its regenerative powers, has been identified in at least 10 known lakes and ponds in the state.

That number is expected to rise as scientists from the Connecticut Aquatic Experiment Station’s Office of Aquatic Species (CAES/OAIS) scour 94 state-owed marinas in search of the worrisome weed, which they fear is spreading undetected.

Time is of the essence to locate, control and eradicate an aggressive subspecies of Hydrilla verticillata, which is unique to the Connecticut River and grows at an astonishing rate of up to a foot a day with long, slender stems that can grow underwater to lengths of up to 30 feet and spread horizontally into thick mats.

Fragments that contain as little as a single whorl of leaves are capable of drifting to other parts of a waterbody and forming new colonies. Left unchecked, perennial hydrilla, which has earned the title of “the world’s worst invasive aquatic plant” and is listed as a federal noxious weed, can completely displace native submerged plant communities, altering fish populations and water chemistry, and threatening bald eagles.

Last summer, East Twin Lake in Salisbury raised alarm when it became the first documented lake outside of the Connecticut River to become infested with a Connecticut River variant of hydrilla. Lake officials suspect it had been thriving undetected beneath the lake’s surface around the marina for several years before being noticed during a routine lake survey. [See timeline here].

Ripples of invasion

Hydrilla, native to Africa and Southeast Asia, has had a rich introduction history into the United States, with multiple subspecies being introduced since the 1960’s. It was first introduced to this country in the early 1950s near Tampa, Fla., when an aquarium plant dealer dumped bundles of the lush, green plant into a canal near his business, and by the early 1990s hydrilla occupied more than 140,000 acres of public lakes and rivers.

In 2016 a new variant of Hydrilla verticillata, subspecies lithuanica, also known as Northern hydrilla, was identified in the Connecticut River, and three years later the CAES surveyed the river from Agawam, Mass., to the Long Island Sound, reporting at least 774 acres of hydrilla.

“The particular strain that is unique to the Connecticut River appears to be much more aggressive and robust than anything we have seen before,” said Gregory Bugbee, who runs the Invasive Plant Program at the Connecticut Agricultural Experiment Station (CAES)

And it is difficult and expensive to manage and eradicate.

“Significant costs are already associated with the impact and maintenance of the prior two subspecies established in the United States since the 1960s and 1980’s,” according to Jeremiah Foley, assistant scientist with CAES.

Why hydrilla management is important

The alarming explosion of Connecticut River hydrilla outside of the Connecticut River has raised significant concerns about its spread inland, threatening the beauty and pristine nature of many of its waterbodies.

The worrisome weed can outcompete native species, replacing habitat for sensitive species including migratory fish. Thick, horizontally-growing mats of hydrilla have crowded out boaters, anglers and those who recreate on the Connecticut River.

Marinas and municipalities have reported that they can no longer access boat slips and docks due to hydrilla infestations, limiting business opportunities. Extensive stands of hydrilla can obstruct swimmers and other water-related activities. The plant can also hurt tourism and impact the value of real estate that depends upon attractive waterways.

“The threat of hydrilla gaining a foothold in our lakes here in the Northwest Corner is an increasing concern of the highest levels.”— John Harney, Salisbury real estate agent

"The threat of hydrilla gaining a foothold in our lakes here in the Northwest Corner is an increasing concern of the highest levels,” said John Harney, a real estate broker with Willaim Pitt Sotheby’s International Realty in Salisbury.

“Twin Lakes commands the highest values for real estate, but this all changes if the lake becomes clogged with hydrilla. I would hope that this is a clarion call to bring all of our resources and attention to solving not only the hydrilla issue, but also to address the effects of overdevelopment.”

Since hydrilla’s discovery last summer in East Twin, the nearby boat launch at Lake Wononscopomuc, has been off-limits to outside boaters to keep the lake from becoming infested, and lake officials there intend to keep it closed indefinitely.

“If you lose this wonderful body of water the town would take such a hit. Property values around the lake will drop if you have a lake you can’t boat or swim in, and it’s not just popular for fishing. This is a very recreational lake for the children,” said Stacey Dodge, Town Grove Manager.

Management and control

The best way to manage hydrilla is to prevent its spread in the first place. Boaters are advised to clean, drain and dry their boats, trailers and equipment after leaving a body to keep hydrilla fragments from entering other lakes or rivers.

Once it becomes established, it is a nightmare to control and can cost as much as $1,000 per acre to manage. Many states are spending millions of dollars annually to control it. Lake Associations and towns can face a staggering rise in management costs, even with state and federal assistance.

Research on this very invasive plant is ongoing, as many biological attributes of this subspecies remain unknown, and it has no natural predators or diseases to limit its population. “Because it’s a new strain, it’s been a slow and frustrating process,” noted the Connecticut River Conservancy’s Rhea Drozdenko, River Steward for Connecticut.

Eradication by harvester is discouraged because even the smallest of fragments can spread and repopulate, and the introduction of grass carp into lakes is not a viable option, according to Foley, because while the fish will eat hydrilla, they will also devour every other aquatic plant within the lake. Biological control, he recently told members of the Twin Lakes Association during the group’s annual meeting at Camp Isola Bella on East Twin, is still in its infancy.

Aquatic herbicides have shown the most promise.

Coming next: A visit to the Connecticut River, where researchers are testing various aquatic herbicides at five sites.