Overview
Unfortunately, the management of invasive weeds have become part of “Lake Life” in NH and in the states surrounding us. The spread of invasive weeds can easily happen when:
- humans move their boats between water bodies without following “Clean, Drain, Dry”
CLEAN off any plants, animals and algae found during your inspection and dispose of it away from a waterbody, and use any cleaning technologies at launch sites before entering, and after leaving a waterbody.
DRAIN your boat, bait buckets, bilges and other equipment away from the waterbody, leaving your boat’s drain in the open position during transport.
DRY anything that comes into contact with the water
- animals and waterfowl either consume or visit infestation areas and then visit other regions of the same lake to other nearby lakes
Currently, Big Island Pond has three main invasive weeds: european naiad, variable milfoil and fanwort. Mitigation techniques for controlling invasive weeds vary by state and type of invasive weed.
NH DES typically recommends a combination of the following for the biggest impact on controlling invasive weeds:
- benthic barriers – elimination of sunlight to plant life by covering area with a barrier
- diver assisted suction harvesting (DASH) – diver essentially uses a water vacuum to collect and move invasive plants and roots to a nearby boat where debris is bagged and later disposed of in a landfill or compost pile
- herbicide application – typically applied during plant’s growth cycle to kill the target plant (actual herbicide varies depending on the plant)
European Naiad (also known as Spiny Naiad)
In the fall of 2019, European Naiad was spotted in the Blueberry circle cove of Big Island Pond. NH DES was contacted and confirmed the presence of this annual invasive weed, just prior to drawdown. AB Aquatics was deployed to DASH the plants. Due to the fragile nature of the plant, DASH activities were immediately halted. Based on the experience of other NH lakes, DES recommended monitoring the cove, as this annual plant rarely came back. European Naiad is known under many names: Najas minor, brittle waternymph, Spiny Naiad and Brittle Naiad to name a few.
In mid-July 2020, Blueberry circle residents confirmed European Naiad was back. In mid-August, 11 benthic barriers were deployed in the cove. Feedback from AB Aquatics and residents suggest that the benthic barriers were not enough to address this issue. NH DES provided guidance and what raw materials they had to deploy fragmentation barriers and Restricted Access buoys for this area. Through the work of BIP volunteers those materials were deployed and more were built and deployed around Turtle Island, a small island across from Blueberry circle cove.
We continue to work with NH DES to understand this new invasive weed. While many NH lakes have experienced this annual invasive weed only one other NH lake has seen a recurrence like BIP has. Northeast Pond found this weed in 2005 with a 41 acre infestation. Three years later, they had decreased the footprint by 50% by using a herbicide and DASH activities.
European Naiad threatens boating, swimming, fishing, and property values for all of us if the spread is not addressed. To learn more about this invasive weed check out some of these sources: Maine Lake Volunteer Monitoring Program , NOAA GLANSIS and Illnois Wildflowers site.
Variable Milfoil
In 2000, variable milfoil was spotted in Big Island Pond. This perennial weed, grows uncontrolled in the Northeast states due to ph levels and with sunlight can grow 3+ inches per day. Big Island Pond has been long been battling this infestation utilizing significant investment with the help of countless volunteer hours, Friends of Big Island Pond and AB Aquatics. Looking at snapshot of the last 12 years in our battle against variable milfoil has resulted in:
- $400,000 dollars spent harvesting around 25,000 gallons of variable milfoil in about 500 DASH days
- the creation of Friends of Big Island Pond, a 501©(3) organization, created by BIP residents. Friends of Big Island Pond was created to established as a funding mechanism to protect the watershed of Big Island Pond.
The deployment of benthic barriers and DASH activities have been successfully used on Big Island Pond forcing back variable milfoil from a large infestation to where we are today – maintenance. Regular DASH activities and our annual drawdown help to control the spread of this highly aggressive invasive weed.
Fanwort
Fanwort has been part of Big Island Pond since the 1950s. While fanwort is considered an invasive weed, NH DES considers fanwort a fundamental part of the BIP ecosystem. Luckily this invasive weed does not spread or infiltrate other areas of the lake. Our annual drawdown helps control this invasive weed.
Long Term Management Plan
New 2026 Long-Term Plan for Managing Invasive Aquatic Plants in Big Island Pond
The New Hampshire Department of Environmental Services has completed an updated Long-Term Variable Milfoil and Brittle Naiad Management Plan for Big Island Pond. The plan explains the history of invasive aquatic plants in the pond, the work completed in recent years, the management methods available, and the recommended approach through 2029.
The full report is detailed and technical. Here is what pond residents and visitors should understand.
Why is this plan needed?
Big Island Pond contains several non-native aquatic plants:
Variable milfoil, first documented in the pond in 2003
Brittle or spiny naiad, first confirmed in 2020
Fanwort, which has been present since at least the 1960s and is now widespread throughout much of the pond
These plants can spread rapidly, form dense growth, interfere with boating and swimming, crowd out native vegetation, and change aquatic habitat.
The plan is not based on the idea that every invasive plant can be completely eliminated. Because Big Island Pond is large and already contains three established invasive species, the realistic goal is to reduce, contain, and manage their growth before they spread further.
What does the plan recommend?
The state recommends an integrated approach rather than relying on one method.
Weed watching and reporting
Trained volunteers will continue checking the pond during the growing season. Early detection is important because a few individual plants are much easier and less expensive to remove than a large, established patch.
Hand-pulling and diver removal
Individual plants and small patches may be carefully removed by divers.
For larger areas, divers may use Diver-Assisted Suction Harvesting, commonly called DASH. This method allows divers to remove plants, including their roots, while collecting the material so that fragments do not float away and establish new growth elsewhere.
Targeted herbicide treatment
The plan recommends targeted herbicide treatment where invasive plant growth is too widespread or dense for practical diver removal, particularly for brittle or spiny naiad.
This does not mean the entire pond will be treated. Treatment areas are selected based on surveys, plant density, water conditions, environmental review, permitting requirements, and the locations of sensitive resources.
The proposed 2026 treatment map appears on page 28 of the plan. It identifies multiple targeted areas around the pond rather than one lake-wide application.
Follow-up surveys
After management work is completed, the pond is surveyed again. Those findings help determine what should be done the following year.
This is known as adaptive management: decisions are based on current conditions rather than following a fixed plan regardless of what is actually found in the water.
Why not simply cut or mechanically harvest the weeds?
Mechanical harvesting is not recommended for variable milfoil or brittle naiad because these plants can reproduce from fragments.
Cutting them without properly collecting the pieces can make the problem worse. A small fragment carried by a boat, propeller, current, or trailer may start a new infestation in another part of the pond.
The plan also explains that annual drawdowns have not been effective at controlling these species. Dredging would be extremely expensive and would not selectively target invasive plants. There are currently no approved biological controls for these species in New Hampshire.
Are native plants supposed to be removed?
No.
Native aquatic plants provide important habitat for fish, turtles, loons, insects, and other wildlife. The purpose of the management program is to target invasive species while protecting the pond’s native plant community as much as possible.
The plan specifically states that no control of native aquatic plants is intended.
What has already been done?
Big Island Pond has used a combination of diver removal and targeted treatment for several years.
The changing treatment acreage does not necessarily mean the problem is simply getting better or worse. Treatment areas can change because of plant location, density, seasonal growth, weather, water movement, survey findings, and the effectiveness of previous work.
What can pond users do?
Everyone who uses Big Island Pond can help limit the spread of invasive plants.
Before moving a boat, trailer, kayak, paddleboard, anchor, fishing equipment, or other gear:
- Clean off all plants, mud, and debris.
- Drain all water from the boat and equipment.
- Dry equipment before entering another waterbody.
- Do not pull suspicious plants unless you know how to collect and dispose of them without creating fragments.
- Report suspected invasive growth to BIPC or a trained Weed Watcher.
A long-term commitment to Big Island Pond
There is no one-time solution to Big Island Pond’s invasive aquatic plant problem. Effective management requires regular surveys, trained volunteers, professional divers, carefully selected treatments, state oversight, funding, and cooperation from everyone who uses the pond.
The updated plan provides the framework for that work through 2029. It also recognizes that recommendations may change as new information becomes available and conditions in the pond evolve.
Residents are encouraged to review the full 2026 Long-Term Variable Milfoil and Brittle Naiad Management Plan below for the treatment history, management recommendations, maps, environmental information, and proposed 2026 management areas.
Prepared by:
NH Department of Environmental Services
March 2022
