Algal blooms of the kind seen on the Shannon lakes in summertime are unlikely to be eradicated unless phosphates are removed from agricultural fertilisers used in river catchments.
That is the view of Swiss and French experts who said the phosphates problem needs to be addressed by all who produce phosphates - industry, town waste-water systems and farmers.
In the State, more than €200 million is being spent under the National Development Plan on sewage plants. Industrial effluent is restricted and monitored by local authorities and the Environmental Protection Agency.
However, restrictions on the use of phosphates and nitrates in agriculture as recommended by a report last year are still the subject of negotiations between the Minister for the Environment, Mr Cullen, and farmers.
But according to the Swiss - who turned around the quality of water in Lake Leman (also known as Lake Geneva) from heavily polluted in the early 1980s to an acceptable bathing and drinking standard - the agricultural element, while actually smaller than that of the towns and industry, is vital.
The experts, members of the International Commission for the Protection of Lake Geneva, said eutrophication - the starving of oxygen in the water - was a big problem in the early 1980s. A similar problem existed in Lake Constance on the Austrian, German and Swiss border, in Lake Maggiore on the Swiss-Italian border and in the Rhine.
International commissions for the protection of all three lakes were set up and the quality of the water has improved to the point where salmon have returned to the Swiss reaches of the Rhine - about 800 miles from the sea - and dramatic improvements have been recorded. More than 80 per cent of the beaches around Lake Geneva are of excellent bacteriological quality and 15 per cent are classed as good quality. Only a few areas still pose a problem.
An engineer with the International Commission for the Protection of Lake Geneva, Ms Aline Clerc, told the Irish expert group that over-fertilisation and erosion of agricultural soil must be avoided.
She said a number of measures had been successful, including a ban on phosphates in detergents and imposing a domestic charge for water which included a cost calculated for waste-water treatment. Citizens of Lausanne, for example, pay about €2 per cubic metre of water, with 42 cent of that being the calculated cost of the waste-water treatment plant.
Another important aspect outlined by Ms Clerc was the fact that less than five per cent of the resident population were on "individual treatment" works or septic tanks.
