Dumping of material close to water courses and the direct discharge of effluent from farms, industry and local authorities as well as drainage works were the main sources of water contamination in the south-west last year.
However, illegal poaching with the use of nets as well as legal drift netting was the major source of concern in at least one important angling river in south Kerry.
Most of the fish caught on the Kerry Blackwater had their flesh torn by the nets, a worrying development for the local economy where tourist angling on that river alone is worth €112,000 and increasing.
There were more than 200 complaints of environmental interference with rivers in Cork and Kerry, according to an annual review by the South Western Regional Fisheries Board.
The public was becoming more aware of the "true value and the fragility" of the region's fishery resource, and were more ready to report incidents, Mr Aidan Barry, chief executive, said. That was reflected in the seizure of equipment and thousands of yards of netting by fishery officers.
Slurry and silage accounted for almost 40 of the complaints received, with drainage and gravel removal accounting for 37 complaints. There were 16 complaints of sewage from local authority outlets.
Silage discharge on the River Bride killed 1,000 fish, one of seven fish kills in the Cork region. Herbicides and chemicals used in poaching accounted for other fish kills.
Poaching was a problem in the Kenmare River and Bay area.