Aqua Laguna

Aqua Laguna (アクア・ラグナ, Akua Raguna) is an annual high tide that happens in Water 7. It engulfs the lower part of the city with a very big wave. Every year during the Aqua laguna everyone needs to move to a very high place. After each Aqua Laguna, part of Water 7 sinks. This causes the city to constantly have to be repaired.

In an anime filler episode, it was shown that on the roof of the houses in the lower part there will be salt which is known as the salt from All Blue.

In One Piece Yellow it is revealed that the water that makes up the Aqua Laguna comes from Long Ring Long Land in the once-in-a-year time when the sea level lowers exposing the ring of land connecting the islets among each other. So, it is possible - although never stated - that last year's Aqua Laguna was bigger than usual because of the large extent of sea that was frozen by Aokiji some days before.