Dúchas has commenced an investigation after large numbers of dead birds started appearing on beaches along the north Wexford coast.
The birds - including guillemots, razor bills and rare Manx shearwaters - were found not far from the important breeding colony of seabirds on the Saltee Islands.
The dead birds were washed up along a stretch of coast between Ballymoney and the Raven Point, just north of a number of Specially Protected Areas (SPAs) for birds and in a region well known for important mussel fisheries.
The dead birds were preceded by abnormal amounts of shells and crustaceans not normally found in the area.
There was no oil visible on the birds and no obvious cause of death, except that some were bleeding from the beak.
It is understood that a Dúchas ranger overflew the area with the Coast Guard last week.
Results of post-mortems on the birds are expected early next week, but initial assessments of the symptoms would appear to suggest poisoning.
Ms Karin Dubsky of Coastwatch said the appearance of the crustaceans indicated some kind of disturbance to the seabed, which, allowing for tidal conditions, she pinpointed as being somewhere in the region of Wexford Harbour.
According to her, the appearance of lobster and molluscs "would indicate some kind of a dredging event" .
Coastwatch ruled out the possibility of a tanker releasing effluent or oil, because of the unmarked nature of the birds.
Significantly, all the birds which were found were fish-eaters, and the possibility that they were poisoned by a natural food source has not been ruled out.
According to Ms Dubsky, this explanation is particularly worrying with regard to the adjacent Saltee Islands, which are breeding grounds for the birds.
Guillemots, which have just started their breeding season, lay just one egg each year, a factor which makes the loss of about 100 of them a "massive blow" for the colony, according to Ms Dubsky.
Last Monday a fine waxy material was also visible on beaches in the area, and one theory advanced by Coastwatch is that a dredging operation may have unintentionally uncovered material which had been buried on the seabed for some time.
"It would be possible for old sins to have been dredged up, normally capped by more recent depositions.
"This is my hunch. It is not proven," she said.
