A long stretch of Tipperary's Lough Derg shoreline has been declared unfit for bathers because of high concentrations of algal bloom.
In March, Lough Derg was cited by the Minister for the Environment and Local Government as a location in which Government anti-pollution policies were working.
Now, Tipperary North Riding County Council has erected signs at the main lakeside resorts, declaring the water unfit for bathing, as a precautionary measure. "If I was a parent, I wouldn't allow children to go swimming in the lake, because it could be dangerous," a council spokesperson said.
A routine sampling test on Friday detected algal bloom at numerous bathing areas and inlets on the Lough Derg shoreline.
"Sampling and testing is ongoing and the results should be back sometime early this week," the spokesperson said. "Basically, this is an algae that is more concentrated than others, so it is important that the council issue a precautionary notice. It is better to be careful than ignore it."
People are advised not to swim in the lake or drink water from it.
Father Sean MacDonagh, the chairman of VOICE (Voice of Irish Concern for the Environment), called for an authority to be established to monitor and manage pollution in the Shannon catchment area. "It is known for years that Lough Derg is being polluted by domestic, industrial and agricultural waste," he said. "This is worrying, because people in Nenagh are drinking water which comes from Lough Derg."
The council spokesperson said the indications were that Nenagh's drinking water, which is taken from the lake, was of a satisfactory standard.
Nenagh Chamber of Commerce expressed concern at the pollution. A spokesman, Mr Peter Ward, emphasised that tourism in the region depended on water quality.
Algal bloom suffocates fish after entering their gills and can be poisonous to people. It usually occurs in warm, dry weather. Sewage and the use of fertilisers, leading to an excess of nutrients in the water, are among the causes of the problem.
On a number of occasions over the past nine months improvements in water quality at Lough Derg have been cited as a vindication of the Government's catchment-based strategy, which is part of a programme of investment in sewage facilities throughout the State. This, in turn, is part of a £3 billion provision in the National Development Plan to improve the handling of water.
Farming continues to be regarded as the largest single source of lake and river pollution. Earlier this year, Mr Robert Molloy, Minister of State for Housing and Urban Renewal, urged local authorities to enact by-laws to combat water pollution from farms. There was a reduction of 20 per cent in the use of phosphorous fertiliser in the three years to 1999.
The Minister for the Environment, Mr Dempsey, has also struck a voluntary agreement with the detergents industry to phase out 95 per cent of phosphate-based laundry detergents by the end of 2002.
A spokesman for Mr Dempsey said last night the Minister was awaiting full information on the situation at Lough Derg.
In May, Mountshannon marina on the Co Clare shoreline of Lough Derg was presented with a Blue Flag - a quality mark which takes into account water quality, beach management and facilities for visitors.