For Immediate Release
Date: September 29, 2023

New to New Hampshire – Invasive Spiny Water Flea Confirmed in Lake Winnipesaukee

Concord, NH – This summer, state biologists from the New Hampshire Department of Environmental Services (NHDES) documented the presence of a new aquatic invasive species to New Hampshire. The spiny water flea (Bythotrephes longimanus) was documented on September 13 in the deepest location of Lake Winnipesaukee, in the Broads in Gilford, New Hampshire. Subsequent sampling also confirmed spiny water flea presence in Alton and Wolfeboro areas of the lake. State biologists believe this is a recent infestation.

The spiny water flea is a microscopic animal, also known as zooplankton, that is native to Europe and Asia. Spiny water fleas were first introduced to the United States to the Great Lakes in the 1980s. The nearest locations of other spiny water flea infestations include Lake Champlain in Vermont, and Lake George and a few other waterbodies in New York. The tiny animal was likely introduced by transient boaters who visited a waterbody with an existing infestation. Live organisms or eggs were probably transported to Lake Winnipesaukee on recreational or fishing gear or in the live well or bilge of a boat.
There are no treatments available to control this species once it is established, therefore the best, and only management option, is preventing introduction into uninfected waterbodies by cleaning, draining and drying all vessels and recreational gear after leaving a waterbody as required by state law (RSA 487).

The spiny water flea is not harmful to humans; however, it can be a nuisance when it builds up on fishing lines. It can also negatively impact aquatic food webs by changing the plankton community which can, in turn, influence fish populations. “Some of our native fish species could be impacted by this,” said John Magee, Programs Supervisor with the Inland Fisheries Division at the New Hampshire Fish and Game Department. “At high densities, the spiny water flea can outcompete native zooplankton on which some of our native fish species rely.”

NHDES biologists have been monitoring for this species for the past eight years, anticipating eventual detection in New Hampshire. “Invasive species are very good at spreading to new locations,” said Kirsten Hugger, an Aquatic Ecologist with NHDES. “We anticipated there was potential for introduction to Lake Winnipesaukee due to boater traffic, which is why we initiated a monitoring program in 2016. However, it is still surprising and disappointing to have confirmed that spiny water flea is in New Hampshire.”  

Non-native aquatic invasive animals are those that are not naturally found in New Hampshire’s lakes, ponds and rivers. Because they are not native, they have few predators or diseases, allowing them to grow quickly and dominate the freshwater systems. Aquatic invasive species, whether invasive plants or animals, can cause impacts to native aquatic species, reduced shorefront property values, water quality impairments and problems with the aesthetic and recreational values of waterbodies. Further expansion of the spiny water flea to other waterbodies in New Hampshire is likely over time.

Boaters and other on-water recreation enthusiasts are urged to be aware of their role in the spread of aquatic invasive species, large or small, and practice good lake stewardship activities, specifically:

Clean off any plants, animals and algae found on boats, trailers, and other recreational gear, and dispose of it away from a waterbody. This includes anything attached to fishing line, tackle and nets and other equipment used in fishing activities. Pressure washing with hot water is recommended. For fishing and other gear, inspect and remove any organisms you find and wash with soapy and/or hot water. Dispose of unwanted bait and associated water in the trash or on land away from water, rather than dumping it in the waterbody.

Drain your boat, bait buckets, bilges, live wells, and other water-holding equipment away from the waterbody, leaving all drains in the open position during transport.

Dry anything that comes into contact with the water for at least five days.

For more information or to report a potential new infestation, please contact Kirsten Hugger at or John Magee at