Mr Edwards said wintering waders and wildfowl numbers were “starting to build” at the reserve, which is jointly managed by the Royal Society for the Protection of Birds (RSPB).
“We were hit by the initial outbreak of bird flu a couple of years ago and this had a devastating impact on our breeding seabirds,” he said.
“Now there’s this new threat just as our wintering species arrive.”
Mr Edwards said the RSPB would ask visitors to report any dead birds on the reserve to its team and not to touch any carcasses.