The Coastguard Service has confirmed that a quantity of oil has leaked from sunken vessel off the Connemara coast.
A spokesman said it received a report late last night of a possible pollution threat west of Carna near Mweenish Island.
A Coastguard helicopter from Shannon was sent to survey the stretch of water earlier this morning.
The spokesman said the service was still assessing the extent of the spill and if the leak was continuing.
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He said if the material in the water turns out to be heavy oil a clean-up operation would be needed.
The pollution was spotted last night by a warden from Galway County Council who was in the area investigating a diesel spill.