Introduced into the United States by aquatic gardeners in the late 1800s, the water chestnut flourishes in shallow, slow-moving bodies of water, such as lakes. A one-acre patch can increase to a hundred acres in a year, crowding out vegetation that fish and other aquatic life rely on for food. The leaves absorb sunlight, causing the water to heat up.
Worse, when the annual plants die and sink to the bottom each fall, their decomposition depletes the water of vital dissolved oxygen.
Water chestnuts don't just cause environmental damage; they also interfere with human recreation. Fishing, boating, and swimming can become almost impossible, and the plant's seeds, sharp enough to pierce shoes, pose an additional hazard.
As far as anyone knows, nothing eats these plants, said Kelly Germann, the conservancy's conservation coordinator. It's up to humans to keep them in check.
Despite removal efforts - some with six-digit price tags - the species is now established throughout the Middle Atlantic and New England regions. But so far, it's made only tentative inroads in New Jersey and Pennsylvania.
The volunteers are trying to prevent Lake Delmont's water chestnut population - one of the state's largest - from taking hold and spreading down Unami Creek, which flows into and out of the manmade lake.
In mid-August, every remaining plant will drop up to 20 mature seeds - each of which can produce 15 cabbage-size rosettes - into the mud below. Scientists think they can remain viable for a decade. A few plants have been spotted downstream.
On this day, Germann wades into the murky water, pulling a metal cable behind her. She and volunteer Michael Shaw, 11, encircled a large clump of floating rosettes with the cable, clipping it to the hitch of Maslany's pickup. Maslany, who directed the U.S. Environmental Protection Agency's Air and Water Protection divisions at its mid-Atlantic regional office before retiring seven years ago, eases the truck uphill, dragging the plants onto the shore.
Eight other volunteers are in canoes and rowboats, uprooting the floating vegetation by hand. Wearing work gloves, they pile plants into boats and deposit them on the shore to rot.
The work is slow, but satisfying, like weeding a garden.
No one knows exactly how the species got into the lake. Someone may have decided it would complement the lake's natural flora, or dumped it thoughtlessly from a home aquarium.
The conservancy first learned of the invasion in fall 2007, and a year later received a $9,000 grant from the Fish and Wildlife Service to address the problem. Germann plans two to three years of intensive removal, then 10 more of low-level maintenance. She will also teach the reservation's Boy Scouts and creekside residents to recognize and remove the plants.
Germann thinks there's still time to stop the plant's advance into Pennsylvania - if she can muster enough manpower. So far, she's held three four-hour volunteer work days, each attended by about 10 people. They've managed to remove an acre and a half of water chestnut. Several more sessions are scheduled.
"We're desperate for volunteers," she said, looking out at the vast mats of water chestnut still covering much of the lake's surface.
She emphasized that no experience or special equipment is necessary, and encouraged anyone interested in helping to visit the conservancy Web site (perkiomenwatershed.org) or contact her at 610-287-9383 or firstname.lastname@example.org.
Contact staff writer Karen Knee at 215-854-5728 or email@example.com.