A mussel considered to be an underwater pest has spread to Lough Neagh, it has been confirmed.
Zebra mussels were first found in Northern Ireland in 1997
Zebra mussels can filter between one and two litres of water a day, taking away algae and other organisms which birds and fish thrive on.
The Environment and Heritage Service, said their "potential impact is huge".
Zebra Mussels were first discovered in Northern Ireland in Lough Erne in 1997 and efforts to stop them spreading have been continuing since then.
Since November 2005, scientists have been scouring Lough Neagh to see if the UK's largest freshwater lake has been colonised by the species after five of them were found on the hull of a boat.
"We are greatly concerned that zebra mussels have spread to Lough Neagh and other small lakes not connected to the navigable Shannon/Erne system," Bob Davidson of the EHS said on Wednesday.
"It is imperative that we curtail the spread now and protect other vulnerable lakes identified in the Zebra Mussel Management Strategy such as Lough Melvin, the MacNean lakes, Mill Lough and many others."
The mussels have spread to Lough Neagh
Zebra mussels, which are native to the Caspian Sea in eastern Europe, attach onto the shells of native mussels preventing them from feeding and resulting in their death.
They can also have a damaging impact on facilities which depend on water-intake by blocking pipes which they attach themselves to.
As a result, boats and water treatment plants can be damaged.
They have previously affected private and public water abstraction stations on Lough Erne in County Fermanagh, resulting in modifications at the Killyhevlin Water Treatment Plant costing over £100,000.