High levels of phosphorus on one of the Killarney lakes have led Kerry County Council to put up notices warning of a potentially toxic algal bloom along its shore.
Mr Fergus Dillon, a senior engineer with the council's environmental services section, said the warning notices were a precautionary measure as no actual bloom had occurred yet.
However there was a high risk of a bloom and the algae on Lough Leane, the largest of the Killarney lakes, was "fairly extensive".
"Everything is against us. The phosphorus levels are high, in or around trigger level of a bloom. We have muggy weather and low water levels," Mr Dillon said.
Agricultural slurry and fertilisers, detergents, fats and oils from the tourist industry, as well as septic tanks and the council's own lack of proper sewage facilities in outlying villages, have been shown to be present in what is one of the area's most popular tourist attractions.
A three-year catchment-based study identified the control of the spreading of fertilisers and slurry storage problems as one of the principal factors that needed to be addressed.
Most of the septic tanks in the area were also found to be inadequate and not functioning properly.
However, while strict new guidelines for septic tanks have been implemented, agricultural bye-laws have not yet been adopted by the county councillors, despite being drawn up for almost three years.
The clean-up of the lake will cost around €17 million and take some years.