The first and second lines of defense: prevention and early detection of aquatic invasive species

Date: May 06, 2022

New Hampshire has been battling aquatic invasive species infestations since the mid-1960s, when variable milfoil was first identified in the waters of Lake Winnipesaukee. Since then, a total of 91 waterbodies have become infested with one or more types of aquatic invasive species (AIS). These include 11 river systems and 80 lakes and ponds across the state. Adding all those individual infestations up, New Hampshire can count a total of 117 types of infestations, with some waterbodies plagued by up to six different AIS. The image above shows one site in southern New Hampshire with intermixed growth of variable milfoil and fanwort, with their long stems taking up much of the water column, pushing out native species and affecting natural habitat for aquatic life.

The rate of infestation used to be multiple new infestations a year, but thanks to both prevention and early detection efforts, we have been able to reduce the rate of spread to one or less new waterbodies a year for the last several years.


Prevention efforts include signs at boat launches, outreach and education efforts with various groups, and strategic laws and rules to prevent the overland spread of AIS in the aquarium and water garden trade bringing potentially harmful species into the state through retail trade, and with transient boats moving species between waterbodies. “Clean, drain and dry” messaging has also been used for several years to inform boaters of actions they should take to decontaminate and disinfect their recreational gear.

A program that has resulted in a significant reduction of AIS spread is the Lake Host Program, run by the New Hampshire Lakes Association (NH LAKES), funded in part by grants from NHDES and other sources, as well as volunteer time from both public and private entities. The Lake Host Program is an outreach and inspection program that puts staff at 100 of the highest-use boat launch sites in the state.  Lake Hosts are trained by NHDES and NH LAKES to educate boaters about AIS and their impacts and spread, and they also conduct courtesy boat inspections to spot and remove AIS before the boater launches and after they pull out of a waterbody. Each year, the Lake Host program reaches more and more boaters, and the last few years they have exceeded 100,000 interactions and inspections each year. While inspections have gone up, it is encouraging to see the rate of “saves” go down (a save is when an AIS is removed from a boat or trailer), an indication that outreach and education efforts are paying off, and boaters are doing more self-inspections to remove tag-along species from their vessels.  NHDES awards over $260,000 a year for these efforts, and those grants in turn leverage several hundreds of thousands of dollars from other sources to support this important program.

Early Detection

Early detection efforts are largely done thanks to an extensive network of volunteer monitors throughout New Hampshire. Over 300 waterbodies (both lakes and rivers) in the state participate in some type of volunteer monitoring, including Weed Watching, which is NHDES’ program to train volunteers how to monitor their waterbodies for AIS, to find new infestations early, and report them to NHDES for verification and action. NHDES field biologists have also found new infestations through their daily work on waterbodies across the state during the growing season.  

Historically, many infestations were found when they were already covering acres of a waterbody, when involved and long-term management were required to get infestations under control, and eradication was unlikely. Now, with a trained network of volunteers and busy field biologists, many new infestations have been caught in early stages, when eradication is still feasible with fast and strategic management efforts. Some of our volunteers have even found new infestations at a single plant stage, which is remarkable!

New Hampshire continues to stay current with the science of AIS, so that we can continue to expand programs as needed to address current and future threats to our surface waters from these species.

If you are interested in keeping an eye out for AIS by becoming a Weed Watcher, please email We have developed a book of common aquatic plants, which includes native plants as well as aquatic invasive plants to be on the lookout for. Links to more information, including fact sheets, plant identification tips and maps of infestations can be found on the NHDES invasive species webpage.

A New Program

New Hampshire is also continuing to work to educate boaters who come into New Hampshire from other states, where different AIS are present, so that they don’t bring additional species into the state when they visit New Hampshire’s waters. In 2021, an out-of-state boater decal program went into effect, requiring boaters with vessels registered in a state other than New Hampshire to purchase an invasive species decal. An online vendor site was established with information about AIS and a portal to purchase a $20 decal, which they affix to their vessel. The platform allows us to gather information about the number and types of vessels visiting New Hampshire from out of state, and proceeds from decal sales will be used for prevention and control efforts for AIS infestations in New Hampshire. This program is still growing, but we hope that it will help continue to educate transient boaters about the role they play in keeping waterbodies free from AIS.

It’s Boating Season

Boating season is already underway in New Hampshire. NHDES asks all boaters to be aware of the threats posed by AIS, and to help do their part in preventing the spread of AIS.

It’s as simple as this:

  • CLEAN off any mud, plants, animals and algae from boats, trailers and equipment.
  • DRAIN your boat and equipment away from the waterbody.
  • DRY anything that comes into contact with the water.

Any plants, animals and algae found during your inspection should be removed and disposed of away from a waterbody.