Climate and environmental changes are having noticeable effects on Ireland's rivers, lakes and fish stocks, according to the Central Fisheries Board.
CFB Chief Executive Dr Ciaran Byrne also said that rivers were bound to be affected by building work close to them.
Scientific and research staff at the CFB have been dealing with increasing reports of unusual fish species turning up on the Irish coast, possibly due to warming of the oceans.
It is also now investigating changes in the movements of fish in the rivers.
Dr Byrne, who was formerly the board's director of research and development, said that these are being studied by its staff because of increased concern about their impact.
He also cited the threat to major areas such as Lough Corrib, where a battle is still being fought to prevent lagarosiphon, a plant which came in from abroad, threatening to choke it.
Dr Byrne said that the possibility of further temperature increases in the oceans was a reason for concern and the board was studying ways in which the country's rivers, lakes and fish stock could be protected.
