Enrichment of Irish lakes and rivers probably represents the most serious environmental pollution problem currently affecting the State, with indications the problem will worsen, according to the report.
The scourge of eutrophication suggests that preservation of waters of high ecological quality will only be accomplished by restrictions on intensive farming in key river and lake catchments.
Such a policy seems justified in the large western lakes such as loughs Corrib and Mask. "Failure to do so is likely to lead to situations like Lough Sheelin in Co Cavan, a renowned trout lake which has been badly impacted by pig-farming development."
While enrichment with plant nutrients in the form of phosphorus and nitrogen is moderate in many cases, resulting changes lead to a decline in stocks of game fish (trout and salmon).
Healthy populations of these fish are an important indicator of overall quality of surface waters, the report says. Moreover, there is now evidence of enrichment in 35 per cent of lake area surveyed and signs of stocks decline linked to eutrophication.
Agriculture is responsible for almost 75 per cent of inputs, but as economic activity increases, potential sources of phosphorus losses to water also increase - for example through increased use of detergents and fertilisers.
Also, discharges from urban waste water treatment plants and unsewered industry are likely to be major enriching factors during periods of low water flow and high temperatures when plant growth (which reduces oxygen supply) is most favoured.
Incorporation of phosphorus removal facilities in treatment plants discharging to inland waters may be required to ensure loads are minimised at critical periods. This may prove to be a more profitable use of resources than the provision of secondary treatment facilities in coastal towns and cities.
Phosphorus removal "is now part of the price that must be paid if the State's rivers and lakes are to retain their status as primarily game fish waters and will be needed, in any event, if the water quality targets in the proposed EU directive on water management are to be met," say the authors.
