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Invasive Spiny Waterflea

image of waterfleas resting on a human finger
Tiny waterfleas resting on the tip of a human finger

Spiny waterfleas (Bythotrephes longimanus) are aquatic zooplankton (small animals) from Europe and Asia that have invaded the Great Lakes ecosystem, as well as some inland water bodies. Adults range from ¼ to ⅝ inch long and they have a single long tail with 1-3 sets of small spines along its length. Infestations of spiny waterfleas negatively impact native fish populations, aquatic habitats, and sports fishing. There is no successful method of control.

Habitat and Current Known Locations

Spiny waterfleas live in fresh water habitats and prefer cold temperatures, but can tolerate both brackish and warm water. They have spread throughout the Great Lakes and have been found in more than ten counties in New York State. Lake Erie, Lake Ontario, Lake George, Saratoga Lake, Lake Champlain and a number of smaller water bodies are infested. The map, below, shows which NYS counties have infested water bodies.

Map showing which counties Spiny waterfleas are located

A cluster of spiny waterfleas on fishing line
A cluster of spiny waterfleas on fishing line

Environmental Impact

Spiny waterfleas eat smaller, native zooplankton that are important food for both small crustaceans and native fish such as perch. In some lakes, they have eliminated native zooplankton from the food chain, causing serious declines in native fish populations. In the Great Lakes, spiny waterfleas have been associated with the decline of alewife.

Spiny waterfleas also interfere with fishing, as their spines catch on fishing line, resulting in clogged fishing rod eyelets and damaged reel systems, preventing fish from being reeled in.

How Spiny Waterfleas Spread

Spiny waterfleas originally arrived in the Great Lakes through the ballast water of cruise ships, tankers and cargo carriers. Ballast water is water taken on or discharged by ships for stability, often resulting in organisms getting caught up in the ballasts and inadvertently moved from one region to another. Spiny waterfleas spread by attaching to fishing lines, downriggers, anchor ropes, and fishing nets and hitching rides to other waterbodies. They can also be transported in bilge water, bait buckets, live wells, and the bottoms of canoes and kayaks.

What You Can Do

Illustration of spiny waterflea and its many spines
Illustration of spiny waterflea and its many spines

There is no known control method for the spiny waterflea once it is introduced, so preventing the spread of this invasive is critical.

  • Clean, drain, and dry your watercraft, trailer, and equipment before and after each use. When possible, use the following methods to fully decontaminate your equipment.
    • Clean the outside of the watercraft and trailer with high pressure (2500 psi) hot water (140ºF) for 10 seconds.
    • Flush the inside of the motor and all compartments (bilge, live well, bait buckets, ballast, etc.) with hot water (140ºF) for two minutes.
    • Soak fishing gear and equipment in hot water (140 degrees F) for two minutes.
  • Dump bait bucket water where it came from or on land.
  • Learn how to identify spiny waterfleas(leaves DEC website)
  • Share DEC's spiny waterflea fact sheet (PDF) or this web page with others.

How to Report

Report infestations to DEC by emailing photos and location information to, or via iMapInvasives (leaves DEC website).

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  • For help with PDFs on this page, please call 518-402-9405.
  • Contact for this Page
  • Division of Lands and Forests
    Bureau of Invasive Species and Ecosystem Health
    625 Broadway, 5th Floor
    Albany, NY 12233-4253
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