noun
seashore party; rocky beach festival
A casual gathering or festival held on a rocky seashore, often involving food, games, and enjoying the coastal environment. Related to 磯遊び (playing at the seashore).
See also: 磯遊び
夏になると、地元の人たちは磯祭りを開いて海の幸を楽しむ。
In summer, the locals hold a seashore party and enjoy the seafood.
noun
fishermen's celebration for a good catch; dragon god festival
A traditional celebration by fishermen to honor the dragon god after a bountiful haul. This sense is more specific and ritualistic than the general seashore party.
漁師たちは大漁を祝って磯祭りを行い、龍神に感謝した。
The fishermen held a celebration in honor of the dragon god after a good haul.
磯遊び refers to playing or exploring at the seashore, while 磯祭り is a more organized event or festival.
Compound of 磯 (いそ, 'rocky seashore') and 祭り (まつり, 'festival'). The second sense likely derives from local fishing community traditions.