It comes about a fortnight after cases were discovered at the mouth of the River Bann, about two-and-a-half miles to the south-west.

Last year along the north coast, there were cases discovered in Portstewart harbour, Portrush harbour, and Castlerock beach.

The discoveries are logged onto a system called Bloomin’ Algae, run by The UK Centre for Ecology and Hydrology, and are then checked to see if they are “confirmed cases”, “probable cases”, or false alarms.