Warning signs amid algal bloom at Lough Muckno

The public is being advised not to swim in Lough Muckno as an algal bloom has developed on the County Monaghan lake.

Warning signs have been erected onsite this week, while a notification was also issued on the official Irish informational website www.beaches.ie

Monaghan County Council advised "do not swim or allow children to paddle if there is evidence of discolouration of the water" as algal bloom can cause illnesses.

During periods of calm and warm weather, algae in lakes may multiply rapidly causing the water to become green - known as Algal Bloom. The algae can rise to the surface to form a visible scum. Monaghan Council warned: "Algal blooms and related scums can also be highly toxic to dogs and other animals. Farmers and dog owners should prevent access of their animals to affected areas and should not allow them to drink, swim or ingest any scum."

Although there are no designated Bathing Waters in the county and Monaghan County Council has no obligation to conduct the sampling of any bathing waters, over the summer months, sampling of a number of popular bathing waters takes place from June to September. Samples are taken at Lough Muckno bathing and water sports area, Greaghlone Lake, Creevy Lake, Emy Lough, Hollywood Lake, Halton's River, Gortawinnmey Lake and the beach area at Lough Major.

Testing for Intestinal enterococci, and Escherichia coli (e-coli), Monaghan Council state: "Monthly samples are taken and analysed by our contracted laboratory. It takes three to four days for the results of sampling to be completed and returned by the lab."

According to the Council, the most recent test results show that all locations with the exception of Lough Muckno Bathing area met the required microbiological standards. Lough Muckno has been classified as “Moderate” under the Water Framework Directive status (2019-2024). However, they note: "Nutrient enrichment is a significant issue for all of these lakes."

The planned monitoring is aimed at providing an overall assessment of water quality, but the local authority cautions "there is no absolute guarantee that on the day that an individual chooses to bathe at one of these locations that there may not be an issue with water quality."

Council experts explain that water quality can vary significantly during the day, and from day to day, due to the influences of rain or sunshine or the number of bathers using the lake at any time. "Bathing water quality is at its most vulnerable after heavy rainfall, or in stormy conditions, which may give rise to higher bacterial counts than normal."

In the event of the detection of a Poor-Quality Result the Council will erect a notice at the site advising not to swim and arrange for a further sample to be taken. All monitoring results are available to view on www.beaches.ie

In recent years, the bathing water quality at Lough Muckno has consistently been poor and has been classified as “Below the Minimum Standard” for the 2022-2025 monitoring period. A do not swim notice is currently in place at this location and will remain in place until the quality meets the required standard.

While the bacterial monitoring results for the Water Sports Area and at Black Island on Lough Muckno have consistently indicated that the bathing water quality at these locations is good, due to the algal bloom it is currently not advisable to swim at any of the locations.