Aggressive invasive plant crowds Bucks reservoir

An invasive species of water plant seems to be spreading in southeastern Pennsylvania.

Water chestnuts–no relation to the ones in your Chinese food–have dense surface foliage that can crowd out other plants and threaten fish life. Their spiky seed pods that wash up on shore can make getting near the water painful for anglers and swimmers.

Conservation workers are waging war on them in Bradford Reservoir, also known as Warrington Lake, in central Bucks County. It’s one of the first places in Pennsylvania where they were identified.

“The surface of the water is 100 percent covered with these plant rosettes, and they become very thick and matted,” said Gretchen Schatschneider, district manager with the Bucks County Conservation District. “If you fly overhead, you almost don’t see the lake, it just looks like an extension of the lawn area.”

Late last month, the conservation group and the county Department of Parks and Recreation used a mechanical harvester on a boat to remove 1,500 tons of the weeds, which cleared about a quarter of the surface area of the 22-acre lake.

Schatschneider said they may use a herbicide to remove more of the weeds next summer.

The species was reported at Westtown Lake in Chester County for the first time this summer. The plants, originally from Eurasia, likely spread locally when the barbed seeds get stuck to waterfowl, people, or boats.

“Like all good invasive species, they are very aggressive,” said Morris Arboretum botanist Timothy Block. “These things can very rapidly become a problem even though they may historically have been present in very small numbers.”

Block said he is worried that the plants are spreading down a Montgomery County creek that eventually flows into the Schuylkill River.

They are “probably within less than a mile of the confluence of the Unami and Perkiomen creeks, and once the plant reaches the Perkiomen Creek, there’s really nothing to stop it from flowing downstream into the Schuylkill River,” Block said.

The plants are fairly easy to spot and remove by hand if there are just a few of them present. However, they spread rapidly and become dense and hard to manage if not caught early.

Fred Lubnow, director of the aquatics program with Princeton Hydro, an environmental and engineering consulting firm, said the water chestnut has become a primary concern in the past few years.

“In the last I’d say two to three years we’ve really seen it appear in a lot of places on either side of the Delaware River,” Lubnow said.