The 75-year-old was recovered unconscious from the water at Tywyn, by a crew from Aberdovey RNLI Lifeboat at 16:14 BST on Saturday.
He was flown to hospital by the coastguard rescue helicopter but later died.
The girls were taken to hospital as a precaution.
In a separate incident, three people including a 16-year-old boy and a 14-year-old girl, were rescued from the sea in Harlech at about 15:30 BST on Saturday.
Harlech Coastguard team, Criccieth RNLI Lifeboat, North Wales Police and paramedics were involved in the rescue.
North Wales Police warned people to take extra care in the sea and to avoid taking risks.
A man has died after attempting to rescue two teenage girls who got into difficulty in the sea in Gwynedd.