Ossipee Lake Milfoil


Every state is chchallenged by invasive aquatic species. In New Hampshire the challenge is variable milfoil, a fast-growing indestructible non-native weed that entered state waters in the 1970s and is now found in 73 lakes, rivers, and ponds. Milfoil is spread by boats, whose propellers cut it into fragments that are carried away by water currents. A single fragment can travel for miles and start a new infestation that can be small and measured in feet, or large and measured in acres.

Ossipee Lake is infested in ten locations. It was first discovered in Danforth Pond in the early 1980s, from where it spread to Danforth Brook at the mouth of Broad Bay. It was subsequently found in Phillips Brook, where it migrated to Leavitt Bay in multiple locations in the vicinity of Loon Island.

Milfoil is now also found in Portsmouth Cove, Pickerel Cove, and in the Ossipee River, above and below the dam. In 2012 it was found for the first time in the big lake, near the mouth of the Pine River. Click here for a map of all the infested locations, as provided by DES.

Control Methods

Variable milfoil can be controlled but cannot be eradicated. In the 1980s and 1990s, lake residents, some from Broad-Leavitt Bay Association, organized to pull milfoil from the lake during the annual drawdown. In 2003, Ossipee Lake Alliance arranged for a state-managed chemical treatment of the dense milfoil in Philips Brook, and then arranged for Ossipee Lake to be the first in the state to experiment with using professional divers to remove weeds.

Today, Ossipee Lake’s milfoil management plan uses a blend of methods, from professional hand-harvesting by divers to state-sanctioned chemical treatments to suction harvesting, which uses gas-powered vacuum devices to pull weeds out by their roots. The management plan is based on recommendations by the state, and is overseen by the milfoil subcommittees of the Freedom and Ossipee conservation commissions.

The Cost of Milfoil Control

Controlling milfoil is expensive; and since the weeds cannot be eradicated, finding funds to pay for control is a never-ending process. After forming in 2003, Ossipee Lake Alliance began seeking state and town funds to pay for milfoil control. The Alliance successfully sponsored warrant articles to create town milfoil funds in Freedom and Ossipee, and worked closely with local select boards and conservation officials to obtain maximum state funding assistance. This work continues under the direction of the Freedom and Ossipee conservation commissions.

In 2013, the Alliance redoubled its efforts to create awareness of the states lack of a comprehensive long-term plan to pay for milfoil control. We encouraged and supported the launch of a statewide coalition whose goal is to secure legislation that addresses the funding issue. Information about this effort may be found in the News section of our website.

Milfoil Prevention

Ossipee Lake Alliance also works with state and local groups to keep new milfoil from entering the lake. Our Exotic Species Prevention program is an ah-hoc partnership with boat ramp owners to ensure that boaters voluntarily inspect their craft before entering the lake. Our milfoil prevention pamphlet shows the locations of infested areas and is available at ramps and other locations, including town offices. We have also established a Weed Watchers program around the lake. Individuals and groups monitor their shoreline and elsewhere so that new infestations are quickly found and reported. Ossipee Conservation Commission manages the state’s Lake Host program at the town boat ramp on Pequawket Trail. With help from the adjacent marina, which also has a ramp at the site, the Lake Host effort has increased boaters’ awareness of milfoil and resulted in at least one “save” by preventing milfoil from entering the lake after it was found attached to a boat coming in from another lake.

DES Exotic Species Program

New Hampshire’s Department of Environmental Services is nationally recognized for its expertise in treating and controlling invasive variable milfoil. It is a valuable resource for the work of Ossipee Lake Alliance and the milfoil subcommittees of the Freedom and Ossipee conservation commissions. You can access their Exotic Species Program website here. If you find a new infestation of milfoil, contact DES limnologist Amy Smagula at (603) 271-2248 or amy.smagula@des.nh.gov.