To Sua Ocean Trench

To Sua is a pair of collapsed lava tubes on the south coast of Upolu, filled with seawater that connects to the ocean through underwater passages in the rock. The main pool is 30 metres in diameter and roughly 30 metres deep, with the submerged lava tube exits at around 18 to 22 metres providing a connection to open water for advanced divers. The geology is dramatic and unusual, with light filtering down from the surface opening above while the deeper sections fade into dark rock. Marine life in the enclosed pools is limited but the passages open into reef habitat where parrotfish, surgeonfish, and small reef sharks have been observed. The swim-through nature of the dive requires solid buoyancy skills and comfort with overhead environments; most visitors experience the site as a snorkel or swim rather than a scuba dive, but guided dive access is available through Upolu operators.

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