Many thousands of sprat and other small fish have been washed up on beaches in the northwest, with indications that the algal bloom or “red tide” has also spread to the coasts of Cork and Kerry.
Experts said yesterday the bloom was naturally occurring and was toxic to bottom-dwelling marine species, certain species of fish and shellfish.
Donegal County Council has restricted swimming at Rossnowlagh and Murvagh beaches, with red flags being raised, because of algal bloom off the coast.
It said the situation was being closely monitored and the public would be informed as things progressed.
Marine Institute phytoplankton expert Joe Silke said that the bloom was naturally occurring, it was not associated with pollution, but it contained a “toxic irritant” that damaged gills of shellfish, fish and invertebrates.
The institute said “lower levels” had also been reported on the Galway and north Clare coasts and also in Kenmare, Bantry and Dunmanus bays.
Samples will continue to be monitored.
More information is on the Marine Institute website marine.ie/habs