Landscapes across New Hampshire are being transformed by invasive plant species. In the upper Merrimack watershed, Purple Loosestrife, Hydrilla, Water Chestnut, Curly-Leaf Pondweed, and Variable Milfoil have invaded our water bodies and shorelands. Because they have no insects that feed on them or diseases from their native areas, these invading species crowd out native vegetation and become the dominant plants. This imbalance has a profound effect on the upper Merrimack ecosystem. Wildlife that depends on native plants for shelter and food now must relocate or cannot survive. Water bodies that are choked with these species can make boating, fishing, swimming, and other recreational uses difficult or impossible.

Some of these invaders were introduced as ornamental plants while others came to New Hampshire when aquarium owners emptied their tanks of exotic plants. Moving boats between water bodies is another common way of spreading invasive species. In all of these cases, introductions can be prevented by reaching out to citizens and boating enthusiasts and providing them with information and tools so that they don’t unwittingly introduce invasive plants to the upper Merrimack.

The economic cost of invasive species is high. Billions of dollars have been spent on the control and eradication of these invaders. It is more cost effective to monitor the watershed for invasive species and eradicate them before they become entrenched. To preserve habitat and the region’s natural heritage early detection coupled with rapid response is the best strategy for preventing the spread and establishment of invasive species. Conservation groups, nursery professionals, and Cooperative Extensions are collaborating in efforts to identify and control invasive plant populations.

GOAL 13: Colonization by invasive plant species in the upper Merrimack watershed is controlled so that biodiversity and healthy natural systems are maintained.

OBJECTIVE: VGN-1 – By mid-2008, locations along the river that are impacted by invasive plant species will be identified and activities will be specified as part of a comprehensive plan to address protection of native species and restoration of sites with non-native infestations.


  • Work with Natural Heritage Bureau, The Nature Conservancy, and other nonprofits and agencies to review existing surveys or conduct additional baseline surveys to determine areas with invasive populations or are sensitive to invasions.
  • Work with Natural Heritage Bureau, The Nature Conservancy, and other nonprofits and agencies to draft plan address invasive prevention and control in the upper Merrimack watershed. The plan will utilize the early detection / rapid response approach.
  • Maintain an updated list of alternative native plants to replace the invasive plant populations. Distribute lists to local conservation commissions, lake associations and local plant supply businesses.
  • Refer inquiries from the community at large to Invasive Plant Atlas of New England (IPANE) materials relating to invasive species.
  • Encourage training sessions in every community to provide a network of local people that are able to identify invasive species.
  • Identify and incorporate restoration needs and measures into the overall watershed restoration plan with a draft scheduled to be completed by mid-2009.