It is native to fresh waters of Northern Europe and Asia, but has been accidentally introduced and widely distributed in the Great Lakes area of North America since the 1980s.

Bythotrephes longimanus is a cladoceran crustacean (water flea) recognizable with its straight tail spine averaging about 70% of its length.

Specimens arising from sexually produced cats have a completely straight and relatively shorter spine.

[2] After genetic analysis, it is now considered to be a form of B. longimanus, making Bythotrephes a monotypic genus, (one with only a single species).

However, the water flea has spread in recent years to many areas throughout Europe, including some ports and inland lakes outside its natural range.

[4] Concern has increased to the impact of this invasive species in the Great Lakes region and other areas it might have been accidentally introduced.

As zooplankton is the backbone of aquatic food chains, this tiny crustacean presents a serious risk to the ecosystem.