“World’s Worst Invasive Plant” Has Invaded Worden Pond

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The Rhode Island Department of Environmental Management (DEM) has announced that the highly aggressive invasive plant, Hydrilla verticillata, has been found at Worden Pond in South Kingstown, the largest lake in Rhode Island and a popular recreational resource. Worden Pond is near the northeast corner of Charlestown and upstream to the Pawcatuck River that forms the norther border of Charlestown.

This is the third waterbody in Rhode Island where the noxious plant has been spotted. It was first identified in Indian Lake in South Kingstown in August, and since then has also been documented at Lake Mishnock in West Greenwich. On Nov. 7, DEM staff visiting the boat ramp to sample for blue-green algae encountered the plant and immediately identified the notorious invader. Hydrilla easily multiplies from small plant fragments and is quickly spread when contaminated boats travel to new waterbodies. DEM is again emphasizing that boaters and anglers should take responsibility to check and clean their boats and gear before and after launching their watercraft in any waterbody.

Hydrilla is often referred to as “the world’s worst invasive plant” due to its rapid growth rate and the several ways it can reproduce to outcompete native plants, creating an enormous mass of tangled stems and leaves where there was once open water. According to U.S. Army Corps of Engineers research, during the first week of its growth hydrilla can grow almost three inches per day, but by the fifth week it can grow 191 inches per day due to exponential branching. Such overgrowth of a plant can drastically alter wildlife habitat and impede recreational activities when motorboats and swimmers have difficulty navigating through the thick plants, and fishing lines are frequently snagged on the vegetation. Hydrilla infestation can also have negative economic impacts on communities, affecting shoreline businesses and tourism as documented by Cornell Cooperative Extension. Hydrilla has proven exceptionally difficult to manage, with the states of New York and Florida spending over $10 million and $30 million dollars each year to control the plant, respectively.

Although the plant will reproduce with seeds or roots, just an inch of stem with a few leaves can grow its own root system to generate a whole new plant. These types of plant fragments easily become snagged on recreational equipment such as boat trailers, fishing line, swimming gear, or water skis. Select hydrilla fragments found by DEM staff at Worden Pond were found discarded in the parking lot of the boat ramp, indicating boaters were taking responsibility to check and clean off their boats and gear after hauling their trailers from the water. The transport of any plant or plant part into or out of any Rhode Island waterbody on boats, vessels, other water conveyances, vehicles, trailers, fishing supplies, or any other equipment is  prohibited. Boaters must thoroughly clean their vessels and equipment of even the smallest attached weeds before and after accessing Rhode Island’s freshwaters to avoid spreading any invasive plants that may hitchhike to another location. With winter approaching, the falling water temperatures have slowed hydrilla growth and the plant fragments have started to break away from the sediment before they begin to float away and die off. Therefore, boaters may see an increase in plant fragments washing ashore this time of year, but these are generally not viable and will soon begin to decay. Regardless, late-season boaters are still encouraged to clean the plant fragments from their boats and gear to stay in the habit of practicing good boat hygiene as hydrilla plants will come back next spring. Boaters should always follow the CLEAN DRAIN DRY approach described below, and to take the pledge to help protect the waterbodies where they recreate by taking the following actions:

– CLEAN: Remove all visible aquatic plants, animals, and mud from all equipment before leaving water access.

– DRAIN motor, bilge, livewell, and other water containing devices before leaving water access.

– DRY everything for at least 24 hours OR wipe with a towel before reuse.

– DISPOSE of unwanted bait, worms, and fish parts in the trash.

Aquatic invasive plants are one of the largest causes of impairment in freshwater lakes in RI. Currently there are over 112 lakes and ponds in the state plagued with at least one species of invasive plant, and at least one invasive plant type has been recorded in 29 river segments, with some have more than one invasive plant species. DEM has documented 14 other different aquatic invasive plant species, the most common being variable milfoil and fanwort, which also spreads through plant fragments. While only these two species are widespread in the state, most of the other invasive plant species are only found in a handful of lakes and boaters must prevent moving these plants on boats and trailers to avoid their spread to new locations. Boaters should check their boat, trailer, motor, lines and other gear for plants, and remove any plant material before traveling. Do not put any plant material removed from vessels into any waterbody but dispose of all plants in the trash or compost far from the water. The most efficient and cost-effective management strategy to control hydrilla is to prevent the plants from moving to, and becoming established in a waterbody, and clean boats are a first line of defense. Before heading to a waterbody, boaters should check if invasive plants have been documented at that location using either DEM’s static map and list of waterbodies by town available online here, or the interactive map on DEM’s environmental resource map under the “Freshwater Aquatic Invasive Plants” layer. Boaters are encouraged to report suspected findings of hydrilla by emailing photos and location details to katie.degoosh@dem.ri.gov. Resources to identify the fragile plant can be found here.

For more information on DEM programs and initiatives, visit www.dem.ri.gov. Follow DEM on Facebook, Twitter (@RhodeIslandDEM), or Instagram (@rhodeisland.dem) for timely updates.

Banner photo from RI DEM shows fragments of hydrilla on the boat ramp at Worden Pond. As water temperatures decrease, boaters may see an increase in plant fragments washing ashore.