Birdwatch Ireland says it has received hundreds of reports of dead and dying seabirds along the east and south coasts in recent days.
Clusters of dead birds have been found in some locations.
Fifteen were found on Morriscastle beach in Co Wexford yesterday, with eight found on Brittas Bay beach in Co Wicklow.
Niall Hatch of Birdwatch Ireland says it seems likely the birds have died from avian flu, which has recently been detected in other dead seabirds by the Department of Agriculture.
The species most affected are gannets but razor bills, guillemots and gulls have also been found dead.
In recent months bird flu has devastated some seabird colonies in the UK, and has also been detected in many European countries.
Yesterday, the Department of Agriculture said 21 cases of avian flu have been confirmed in recent weeks and all but one of them were in seabirds.
The department is awaiting results of tests and has advised the public not to handle sick or dead seabirds.
Poultry owners and keepers of captive birds are being urged to maintain the highest biosecurity standards to protect their flocks.