Variable milfoil (Myriophyllum heterophyllum) has been in New Hampshire since the late 1960s and is currently found in 64 waterbodies throughout the state. It was first identified in Squam during the summer of 2000.
Variable milfoil is a submerged aquatic plant characterized by feathery leaflets surrounding a thick, reddish main stem. Milfoil prefers to grow in relatively calm and shallow (less than 20 feet) waters. Though milfoil can produce seeds, the primary form of reproduction and cause of spreading are fragments that break off the plant and grow roots. Variable is a prolific plant; it can grow up to an inch per day and can reproduce from fragments that are as small as several inches. Boats, wind, current, and waterfowl transport these fragments and spread the plant to previously unimpacted areas. Fragments can also stow away in boats, trailers and fishing tackle where they could potential spread to unaffected bodies of water.
Because of variable milfoil's rapid reproductive cycle and the fact that there is not an abundance of natural predators, this invasive species can spread rapidly through a waterbody. It can displace beneficial native vegetation and quickly become a monoculture. It can negatively impact native species, recreation and even property values around infected lakes.
In 2012 the SLA removed more than 3500 gallons of variable milfoil from the Squam Lakes. This record-breaking year was a result of our successful Squam Conservation Internship Program and our milfoil control boat, Millie, which houses a Diver Assisted Suction Harvester (DASH)--see photo below and left. This unit, designed by SLA Director of Recreation Brett Durham, is the most efficient method we have identified to remove variable milfoil from Squam. The DASH unit has a suction hose that scuba divers carry into large milfoil infestations. While underwater, the divers harvest milfoil by the roots and feed the material into the suction hose. Milfoil material is then transported through the hose where it is processed aboard Millie (photo below and right). The DASH unit allows divers to remove large quantities of milfoil while maintaining underwater visibility. For smaller infestations, scuba divers remove milfoil plants by hand, place the plant material in a mesh bag and carry the bags to the surface. The SLA has also used benthic barriers, herbicides and lake drawdown to manage variable milfoil.
Aquatic Invasive Species Reports
What you can do
- Volunteer! Become a volunteer Weed Watcher or Lake Host.
- Learn to identify aquatic invasive species by participating in our Weed Watcher Morning Program.
- Become more informed on how to identify aquatic invasive species by referring to our online Weed Watcher Kit.
- Become of a member of the SLA. Your membership dues supports the SLA's milfoil management activities.
- Educate yourself and help prevent the spread of invasive species. Visit our Web Links page to learn more.