Only 67 per cent of Irish rivers are now classified as unpolluted. That is 10 per cent less than a decade ago, and reflects a continuing trend of decline in their water quality going back more than 25 years.
More rivers are affected by slight to moderate pollution which has increased due to enrichment, known as eutrophication.
Discharges which have a high content of nitrogen or phosphorus are the biggest contributors to this form of environmental strain on water.
The main causes of enrichment of Irish freshwater are animal manure, artificial fertilisers and, to a lesser extent, sewage, including detergents, all of which can have high phosphate levels.
While the pollution is minor in many cases, it is of concern in view of its potential impact on stocks of pollution-sensitive trout and salmon in both rivers and lakes.
Monitoring of "river loads" in the vicinity of estuaries also suggests increases in nitrate concentrations are continuing, particularly in the south-east region.
While phosphorus can have a detrimental impact on river and lake quality, high nitrate levels pose particular risk to coastal waters.
