UNESCO's General Conference, at its 43rd session in 2025, designated 21 August each year as the International Day for Underwater Cultural Heritage, based on a proposal from Egypt, with the first observance set for 2026. The day builds on UNESCO's work under the 2001 Convention on the Protection of the Underwater Cultural Heritage. The day matters because the world's seabeds hold millions of archaeological sites and shipwrecks documenting thousands of years of human history, navigation, trade and conflict. This heritage faces growing risks from looting and illegal excavation, pollution, damage from deep-sea economic activity, and climate-related changes that threaten the stability of these sites. The day is marked through awareness events organized by UNESCO and its regional offices and maritime archaeology museums, documentaries and exhibitions highlighting underwater discoveries, and discussions on strengthening international cooperation to protect this shared heritage of humanity from disappearing.