LRP - Licenses

LRP - Regulations

LRP - Permits

Recreation - Statewide

Recreation - Trapping

Recreation - Fishing

Recreation - Hunting

Env. Protection - Management

Env. Protection - Emergency

Env. Protection - Resources

To sign up for updates or to access your subscriber preferences, please enter your contact information below.

Spiny Water Flea

Spiny Water Flea (Bythotrephes cederstroemi)

Spiny Water Fleas entered the Great Lakes in ship ballast water from Europe, arriving in the 1980’s. With translucent bodies, only about ¼ to ½ inches in length, individual waterfleas may go unnoticed. However, the species tend to gather in masses on fishing lines and downrigger cables, so anglers may be the first to discover a new infestation.


Regulated areas of Spiny Water Flea
Spiny Water Flea is Prohibited (Red counties)

Other names for this animal include:

  • Common names: Spiny Water Flea
  • Scientific names: Bythotrephes cederstroemi

Ecological threat:

  • Spiny and fishhook waterfleas are predators - they eat smaller zooplankton (planktonic animals), including Daphnia. This puts them in direct competition with juvenile fish for food.
  • Young fish have trouble eating these waterfleas due to their long, spiny tails.
  • The spiny and fishhook water fleas produce rapidly through parthenogenesis, commonly known as asexual reproduction, which means that no males are required and populations can explode in number.

Classification in Wisconsin: Prohibited

Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for Spiny Water Fleas was based upon this literature review developed by the department.


Body:The Spiny Water Flea has a 1/4"-1/2" long, translucent body, making it hard to spot unless gathered in a large cluser. The species is also characterized by a long spine that extends from its abdomen, giving reason for its name. In additon, the Spiny Water Flea has a dark black eye that can easily be seen against its contrasting light body.


Check out the known locations of this species in Wisconsin on the Lakes Species Tracked pages.

  • Known Locations of Spiny Water Flea
  • Control

    Spiny water fleas were found in the Gile Flowage (Iron County) in 2003, Stormy Lake (Vilas County) in 2007, and the Madison Chain of Lakes (Lake Mendota, Lake Monona, Lake Waubesa, and Lake Kegonsa in Dane County) in 2009. See all known locations of Spiny Water Flea in Wisconsin- Locations of Spiny Water Flea

    Unfortunately, at this time no effective strategy is available to control the spiny water fleas once they are introduced to lakes.


    Links for More Information

    Last revised: Monday December 11 201712/11/2012