Signage is advising people to avoid contact with the algae and to keep animals out of the water.
BBC NI agriculture and environment correspondent
Donna Laughlin from Antrim said her husband and his cousin began to feel unwell a day after they spent time in the water in Lough Erne. Ms Laughlin said her family did see algae in the water while they were waterskiing, but they did not realise the danger."It wasn't apparent at the time - we didn't know the risk factors, obviously. But we soon learned about them afterwards," she said.
Armagh City, Banbridge and Craigavon Council said wind direction had pushed the bloom on Lough Neagh south and it had moved from Bartin's Bay to Oxford Island.
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