The discovery of an exotic species of mussel in the lower reaches of the river Shannon created additional problems this year for a massive salmon restocking programme of the middle reaches of Lough Ree by the ESB.
The work of releasing over 1.2 million unfed salmon fry into the lake and its tributaries was carried out without transferring the zebra mussel upriver.
The zebra mussel was accidentally imported into the Shannon in water being used for ballasting ships using Foynes harbour.
Since then this species, which has an incredible breeding rate and causes damage to lock gates, outfall pipes, boats and other submerged equipment, has been found in the upper reaches of Lough Derg.
The zebra mussel damages structures because of the very strong tissue it uses to attach itself to feeding positions. It blocks outfall pipes from sewers and power stations. Irish scientists are hoping to prevent the mussel from getting into the waters of Lough Ree or the Shannon system further north and extra precautions are being taken while the smolt is taken from the Parteen Hatchery near Limerick.
Mr Paddy Barry, who manages the hatchery, said the water used to transport the young fish was filtered through fine screens as a preventative measure to ensure that no juvenile mussels would be transported to new areas of the Shannon catchment.
The £1.5 million fisheries management programme is being co-ordinated this year by Mr William O'Connor, an ESB biologist with wide experience in restocking.
The programme has already seen a total of 800,000 unfed fry released into the River Suck catchment area, which is the largest of the Shannon tributaries.
This is part of a drive to build up current stocks on the Suck, and the objective is to boost returns of adult salmon to the area by 2001.
There has been a major decline in game fish stocks on the Suck over the past 15 years and the river is now regarded as a coarse fishing paradise.
Earlier this month pike from Lough Sheelin, in Co Cavan, were gill-netted on the lake and transferred to a number of lakes in Co Roscommon, some of which form part of the Suck catchment.
Fishing is now one of the major products being promoted in the Midlands by tourism interests.