DANGEROUS INVADER: Hydrilla, a fast-spreading invasive weed currently clogging sections of the D&R Canal, can grow an entirely new plant from a tiny stem fragment. Those using the canal for boating are advised to wash off their vessel after leaving the water to help stop the plant’s spread.

As if the emerald ash borer plaguing Princeton’s tree canopy wasn’t enough, there is another dangerous invader on the move. It’s Hydrilla, a fast-spreading invasive weed currently clogging sections of the Delaware and Raritan Canal.

A posting on Princeton’s municipal website warns, in big, red letters, that Hydrilla, named after Hydra, the nine-headed serpent of Greek mythology because it can grow an entirely new plant from a tiny stem fragment, has arrived. The weed “out-competes native vegetation, and has the potential to significantly restrict flow through the canal and damage the natural ecology,” the notice reads. Those using the canal for boating are urged to follow certain recommendations to help stop the spread of the invasive weed.

“This is a newly-emerging invasive species, and it’s huge in New Jersey,” said Michael Van Clef, stewardship director for the Friends of Hopewell Valley Open Space. The New Jersey Invasive Species Strike Team is a project of that organization. “It is something that is extremely aggressive,” Mr. Van Clef continued. “It can clog waterways. It can ruin recreational activities and mess up the ecology of a body of water. It’s definitely something we don’t want.”

According to information from the New Jersey Water Supply Authority, Hydrilla was was first brought to the United States intentionally to sell as an aquarium plant. It is spread, primarily, by human activities. “Although it is listed as a Federal noxious weed, Hydrilla is often found hitchhiking in shipments of aquatic plants used in water gardens and may be sold by aquarium supply dealers or over the Internet,” the organization’s website reads. “Accidental spread is also commonly achieved by the hitchhiking of small Hydrilla fragments on water vehicles including boats, bait buckets, draglines, motors, and trailers to new water systems.”

Mr. Van Clef advises anyone using the canal for kayaking or other activities to wash off their boats after leaving the water. “Don’t drag it around from there to somewhere else,” he said. “That’s very important. These are aquatic hitchhikers.”

Areas of the canal are currently being treated with a low dose herbicide that the water supply authority says is safe and effective. A company called SOLitude Lake Management has been surveying and assessing the effects of Hydrilla and other invasive species in the canal since September 2016. Hydrilla has been observed in 56 percent of the survey sites.

Anyone who thinks they have located Hydrilla in the canal can report it to the strike team. “We have a phone app. And you can do it very easily if you’re out on the fly,” Mr. Van Clef said. “It looks like some other stuff, so it is very important to get the information to the experts.”

The weed looks harmless enough. But it can grow an entirely new plant from a tiny stem fragment. “When there is a lot of it, it’s a clogged up, giant mess,” Mr. Van Clef said. “It is a big concern.”

For more information, visit njwsa.org or the Princeton municipal website at princetonnj.gov.