The worrying increase in slight and moderate pollution of Irish rivers between 1995 and 1997 is mainly due to manures, slurries and excessive spreading of artificial fertilisers which run off into water and cause eutrophication, an enrichment of water.
The EPA report says while sewage contributes to the problem, it is mainly responsible for a slight increase in river mileage classified as "seriously polluted".
Siltation and other negative effects were responsible for much of the slight and moderate pollution recorded in the west. This was caused primarily by over-grazing by sheep but also by bog and forestry development.
The Avoca river, Co Wicklow, continues to be grossly polluted by toxic mining spoil on its bed for more than a century. There is also serious pollution of parts of the Boyne, Dalgan, Feale, Liffey and Nore, though smaller rivers and streams are more vulnerable to serious pollution.
The EPA notes with concern its analysis of selected sewage treatment plants upgraded during the 1980s; notably in Carrickmacross, Cashel, Castlebar, Mountmellick, Mullingar, Portlaoise, Thurles and Tipperary. With the exception of Castlebar, none of the adjoining rivers has yet recovered satisfactorily.
"Most continue to be over-enriched, either by unintercepted waste inputs or by the continuing excessive phosphorus loading [from sewage or domestic waste water, including detergents] which - with the exception of Mullingar - the treatment plants were not designed to remove.
"This is compounded by poor treatment plant performance in most cases," it says. Without phosphorus removal, "secondary treatment" is insufficient to prevent the rivers deteriorating to the most polluted categories.
"Any further recovery in the above stretches is unlikely in the absence of phosphorus removal."
