On its social media site, the Trout Anglers’ Federation of Ireland (TAFI) reported the outbreak, with pictures of the algae on the major angling and tourist pleasure lake, which is considered the jewel in the crown of Kerry tourism.
The council, which monitors the lake, along with the Environmental Protection Agency (EPA), said the signs are being erected as a precaution.
A major outbreak of the toxic algae on the lakeshore in 2016 led to the death of a number of dogs.
The EPA has said there has been an increased number of queries, in recent weeks, relating to algal blooms in lakes in counties Galway and Mayo, and in the River Liffey, at Ballymore Eustace, and it warns that dog deaths are likely to increase.
Investigations are being undertaken by the local authorities involved and relevant signage is in place, the EPA said.
One of the reports to the agency “relates to a series of dog deaths in the vicinity of Lough Mask”.
EPA staff from the Office of Evidence and Assessment have assisted with the provision of responses, or given guidance on the identification of cyanobacteria to local authority staff, where possible, with some algal material also being identified in the EPA Castlebar Inspectorate to rule out potential toxicity issues in Lough Corrib.
The reported prevalence of toxicity-related dog deaths has increased in recent years, with a significant event in Lough Leane, Co Kerry, in 2016. There is likely to be significant under-reporting, while the incidence of this phenomena is anticipated to increase, the statement said.
Shane O’Boyle, senior scientist at the EPA Office of Evidence and Assessment, said algal blooms are part of the natural cycle in lakes.
However, natural algal blooms are intermittent — when they persist, it indicates there is an external nutrient, such as phosphates, feeding them.
Outbreaks of blue-green algae occur on an annual basis in Killarney. An in-depth study held 20 years ago identified eutrophication, or enrichment by phosphates, as responsible for the toxic algae.
Septic tanks, farming, and forestry are the prime culprits, and a major programme, as well as upgrading of septic tanks and slurry pits, saw a reduction in phosphates from these sources.
Killarney town’s sewage treatment plant, alongside the lakes, has come in for increasing scrutiny, with questions over its capacity and efficiency being raised increasingly at council meetings in Killarney.
An assessment of the suitability of the existing wastewater treatment plant outfall point to the Folly Stream will be carried out by 2021, the council has said.