THE advance of zebra mussels into Northern Ireland’s freshwater lakes has gone a step further with their discovery at Lough MacNean in Co Fermanagh.

Adult zebra mussels were found attached to the shell of a native mussel during monitoring by the Northern Ireland Environment Agency (NIEA) on Lower Lough MacNean.

The government’s Zebra Mussel Control Group spelled out the economic and ecological dangers of this invasive alien species, which has already become established in Lough Neagh, Lough Erne and Lough Derg, among others.

Zebra mussels pose a threat to the natural functioning of a lake system and can cause blocked intake pipes, which increases costs to both water treatment plants and boat users.

The mussels, which are native to the Caspian Sea area of eastern Europe, filter water and produce improved clarity. But in Lough Erne this has altered nutrient cycling and reduced the abundance of phytoplankton – the basis of the food chain. As a result the fish populations have changed.

One of the most noticeable impacts in Lough Erne has been on the native swan mussel, which has disappeared. The improved water clarity has also resulted in excessive growth of native aquatic plants, causing serious problems for recreational water users and affecting the tourism trade.

John Early, of the NIEA and The Zebra Mussel Control Group, said: “Zebra mussels attach themselves on the stony lake bottom but also to any hard surface, such as boats, buoys and water intake pipes, where they can form very dense clusters, and are principally spread by recreational water use.

“It is important that water users are aware of the environmental impacts of zebra mussels. The impacts that have been recorded at Lough Erne emphasise the importance of preventing them from spreading to other unconnected lakes. Prevention of spread is an issue of shared responsibility and we are asking all water users to follow the guidance issued.

“Signage has been placed at slipways around Lough Erne and at Lough MacNean, highlighting that boats and equipment should be carefully cleaned, bilge water drained and any plant material attached to the engine or trailer should be removed.

“I would encourage water users to be aware of their presence and, if they do find them outside the Lough Erne and Lough Neagh system, to report them to NIEA. Reports of all invasive species, including zebra mussels, can be made through the ‘Alien Watch’ section of the invasivespeciesireland website.”

Invasive alien species are organisms from abroad which establish themselves in local habitats where they can damage native species by out-competing with them for food, predating on them, altering their habitat or introducing disease.