Spiny water flea on the increase in New Hampshire’s largest lake

CONCORD — Spiny water flea, an invasive microscopic animal, has increased in number across Lake Winnipesaukee this season, based on feedback from anglers who report fouling of fishing lines with dozens of these animals. The spiny water flea is not harmful to humans; however, it can be a nuisance to anglers when it accumulates on fishing lines.  Boaters and other on-water recreation enthusiasts play an important role in stopping the spread of aquatic invasive species such as these.

The New Hampshire Department of Environmental Services will conduct formal surveys in fall 2024, but early indications show densities of the invasive plankton have increased since its discovery in fall 2023 by state biologists.

State biologists warn transient boaters and fishermen to always clean, drain and dry their recreational gear between waterbodies, but especially after being in Lake Winnipesaukee, as well as the two downstream lakes — Lake Opechee and Lake Winnisquam.  All fishing gear, especially fishing line, should be wiped down and left to dry for at least 24-48 hours before being used in another waterbody.  These organisms spread by moving with transient boats, fishing gear, and other equipment that comes in contact with the infected water.

The spiny water flea, a type of zooplankton, is native to Europe and Asia. They were first introduced to the United States Great Lakes in the 1980s via contaminated cargo ship ballast water. Other Northeast locations of spiny water flea infestation include Lake Champlain in Vermont, and Lake George and a few other waterbodies in New York.  The tiny animal was likely first introduced by a transient boater who visited a waterbody with an existing infestation, and then transported live organisms or eggs to Lake Winnipesaukee on recreational gear or in a water containing structure like a live well or bilge. 

The spiny water flea also has negative impacts on the aquatic food web by shifting plankton communities (microscopic plants and animals), resulting in reduced gamefish population, especially trout and salmon.

There are no treatments available to control this species once it is established. The only management option is preventing introduction into uninfected waterbodies.  Boaters and other on-water recreation enthusiasts play an important role in the spread of aquatic invasive species, and should 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.  At a minimum, rinsing of gear or pressure washing gear with high pressure, higher temperature water is ideal.

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, preferably for 24-48 hours.

State biologists will be monitoring spiny water flea populations in September as part of a routine sampling event. 

For more information or to report a potential new infestation, contact Amy Smagula with NHDES at Amy.P.Smagula@des.nh.gov or 603-271-2248.