People have been warned to not bathe in the two largest lakes of Killarney where there is the appearance of algal blooms, Kerry County Council has said.
The warnings encompass the Muckross Lake, which is popular with bathers.
Toxic algae has been a feature of the larger Lough Leane, the largest of the Killarney lakes, for over 30 years.
A study found the causes of the bloom to be linked to phosphate enrichment due to use of fertilisers in farms, forestry and run off from septic tanks.
Notices to dog owners to keep their pets away from the lake have been erected for some weeks on Lough Leane.
The lake, which is up to 60 metres deep in sections, is fed and also drained by numerous rivers.
Earlier this week the quality of the water in the River Laune, which flows from Lough Leane some 22km to the sea near Killorglin was classed as in "bad condition" by the EPA in their water quality report for 2022.
It was one of only two rivers in the country in that worst water category - the other being the Annagh River in Co Clare.
The EPA said urban waste water was responsible for the poor condition of the Lough Laune water.
The council said that the public should also not swim at Muckross Lake, which has a number of beaches popular with locals, if they see algae.
Dundag beach at Muckross House, and smaller beaches near Dinis have seen hundreds of swimmers over the past number of weeks.
"In light of the current and ongoing warm weather conditions, as a precaution, Kerry County Council has erected advisory signage at a number of locations along the shores of Lough Leane and Muckross Lake to advise members of the public of the potential for an algal growth in the water and on the shoreline," it said in a statement.
While the overall levels of algae are "not of particular concern" at the moment, the council has received reports of localised transient shoreline accumulations of algae at a small number of locations.
"Members of the public are advised not to bathe in water if there are visible signs of algal growth in the vicinity. They are also advised to ensure that they keep their dogs under control as such algal accumulations can be harmful on ingestion by small animals," the council said.
The situation is being monitored closely on an ongoing basis by Kerry County Council.
