Swimmers are disappointed that they can not get into the water as bathing alerts have come into effect on two north coast beaches.
It follows the confirmation of high levels of blue-green algae.
It means swimming is not permitted at Downhill and Portstewart beaches.
Increased levels of algae have been detected at Castlerock beach but no bathing notice is in place yet.
Nicole Morelli is part of the Menopausal Mermaids open water swimming group.
She and her friends are disappointed to not be able to get into the water.
“We had such a great day yesterday, and we were really looking forward to getting back in.
“But it’s better to be safe.”
No other beaches are affected at this time.
In a statement, the Department of Agriculture, Environment and Rural Affairs said the algae had been observed on part of Magilligan, Downhill and Portstewart strands on Monday 22nd September 2025 during regular scheduled monitoring.
It said monitoring would continue and advice would be provided to bathing water operators when required.
The National Trust, which manages Portstewart Strand, said algae had been detected “at a red alert level” and it urged all visitors not to swim, avoid any scum or mats on the shore and to keep pets away from the water.
Blue-green algae has been present in Lough Neagh all summer.
Recent weather conditions have led to portions of the algal mats travelling along the Lower Bann River to the North Coast.
In August, the first algae-related bathing ban on the coast was put into place at Benone.
It was lifted a few days later.
A statement from Causeway Coast and Glens council said: “Council has been made aware that blue-green algae may be present in waters at Downhill Strand.
“Currently beach users are asked to be vigilant to the possible presence of blue green algae.”
The council advised beach users who suspect the presence of blue green algae to avoid playing “with scum or mats on the shore”, avoid letting “animals drink water, eat algae or swim”, and avoid swimming, fishing, wading, boating, and kayaking.
“Pet owners should ensure that their animals do not have access to this water, dogs should be kept on a lead and away from the tide line,” the statement added.
“At this stage council would urge vigilance at Castlerock beach.”
