OUT OF SIGHT, OUT OF MIND. Tangible and intangible cultural heritage assets located in coastal and near-shore underwater environments are under particular threat due to climate change and its impact on water. These threatened sites and practices have served historically to not only feed and employ large and small coastal communities, but importantly have provided the societal and cultural roots that have helped bond them together. Although it is acknowledged that water environments (in the context of this article ‘‘water’’ is taken to mean oceans, seas and inland waters) function as a major global food source (SDG 2 Zero Hunger), and play a major role as a carbon sink (SDG13 Climate Action), water is also a vehicle for commerce and many other ocean activities labeled ‘‘the Blue Economy,’’ all of which are considered of critical importance. However, the societal consequences of damage and loss to underwater tangible and intangible heritage assets and associated practices should not be underestimated. Threatened by sea level rise, with seas estimated to rise by up to a meter by the end of the century, combined with extreme weather events (Gregory et al. 2022), it is anticipated that there will be significant loss of these assets with social and cultural consequences. In extreme circumstances, the very existence of some coastal communities and Small Island Developing States (SIDS) is also at risk. Therefore, how to value, protect and manage these often “unseen” underwater cultural heritage sites sustainably is of vital social and cultural importance.