Zebra mussel

Dreissena polymorpha


Photo credit: ©Paul Beckwith BWW
Dreissena polymorpha
  • Slow rivers, canals, docks, lakes, reservoirs and sometimes water pipes and cooling systems

  • The zebra mussel has a distinctive stripy shell and individuals are small, growing up to 3-4 cm in length. Unlike other freshwater mussels, the zebra mussel attaches to hard surfaces using byssal threads. Zebra mussels typically live for two to three years. They will settle on a wide range of surfaces including rocks, anchors, boat hulls, intake pipes, unionid mussels and plants. Dead shells can be found on the bed of water bodies or washed up on the margins, sometimes as single shells but occasionally, as in life, with two shells joined. Even when dead, the shells retain their stripy appearance.
  • Download N.I.E.A. ID guide

Origin and Distribution:
  • Originally from the Caspian and Black Sea region but has become invasive in Europe since the late 1700’s after the construction of an extensive canal network. Zebra mussels are now present in Sweden, Finland, France, the former USSR, Germany, the Netherlands, Italy, Ireland, Switzerland, the United Kingdom, Spain and North America.

  • Changes in nutrient cycles.
  • Reduction of phytoplankton.
  • Increased water clarity.
  • Increased plant growth around lake margins.
  • Reduced zooplankton.
  • Population declines of native mussels as zebra mussel colonise their shells.
  • Changes in fish populations.
  • Blocks water intake pipes.
  • Attaches to the hulls of boats and block boat engines. 

How did it get here?
  • The zebra mussel probably arrived in Ireland in 1994 attached to the hulls of second-hand boats imported from Britain or the Netherlands. This species then were spread into Northern Ireland.

Is it found in Ireland or Northern Ireland?
  • It is present in Ireland and Northern Ireland.
  • More information can be found at NBDC and NBN Atlas NI.

You can help by reporting any sightings:  

Static Distribution Map as of December 2019 - Courtesy of CEDaR

    • Do not introduce zebra mussels to new sites
    • Prevent fouling of boats and equipment
    • Clean all equipment including boats before moving to new waterbodies. See Check Clean Dry for more information.
    • Do not move ballast water between waterbodies
    • Report all sightings.

Current Legislation Position:
  • Dreissena polymorpha is listed in Schedule 9 of the Wildlife (Northern Ireland) Order 1985 and as such, under Article 15 it is an offence to release or allow this species to escape into the wild.

Species Related Files:

Invasive Species Ireland

Invasive Species Ireland