Leitrim lake is 'susceptible to algae blooms' due to it's shallow nature
Leitrim County Council - “Due to the shallow nature of Keeldra lake and its capacity to warm up faster in periods of warm weather, this leaves this lake more susceptible to algae blooms.”
Swimming was banned at Keeldra Lough earlier this month after the detection of elevated algae levels and the Leitrim Observer contacted Leitrim County Council to find out out more about the reasons behind the elevated levels and what is being done to address them.
This week, a response from the Leitrim County Council said: “In 2025 a new wastewater treatment system was installed at Keeldra Lake to treat discharge from the existing amenity facilities. This system incorporates tertiary treatment using willow beds.”
It continued that Leitrim County Council have also carried out Septic Tank inspections in 2025 in the vicinity of Keeldra Lake and some follow up inspections are to be carried out in 2026. “Any Septic Tank issues arising from these inspections will be pursued by Leitrim County Council to ensure remedial works are carried out.”
The response came after swimming was temporarily banned at the lake however a local who lives beside the lake told the Leitrim Observer that there were no signs of algae on the lake and there rarely is.
Damian Brennan told the Leitrim Observer that there were no “obvious signs of algae on the lake this morning (Thursday, 11 June) and there were two people swimming in the lake yesterday. “
Temporary bathing restrictions were put in place on the lough after the detection of elevated algae levels in a water sample taken on May 25, 2026.
Mr Brennan said that he didn’t see “any big difference” in the lake compared to previous years. “I haven’t noticed any algae on the lake here so far but that’s not to say it wasn’t there on a day I wasn’t around. People swim there and a lot of people fish on the lake and occasionally, you might see a trace of algae on a calm day but that’s really about it.”
The response continued that Leitrim County Council will continue to monitor the measures implemented above to determine their long-term benefits. “It is important to note that there may still be nutrients embedded in sedimentation in the lake which have the potential to create further outbreaks of algae blooms. Due to the shallow nature of Keeldra lake and its capacity to warm up faster in periods of warm weather, this leaves this lake more susceptible to algae blooms.”