Many sites, bearing testimony to important historic events, battles, the slave trade, natural disasters, and revolutions, are to be found on the bottom of oceans, rivers and lakes. The sites and shipwrecks of the battles of Salamis, Trafalgar, Lepanto, and Abukir and of the earthquakes that submerged Port Royal, Jamaica, and parts of Alexandria, Egypt, are just some examples. The remains of Herakleion, Baiheliang, as well as countless Stone Age settlements in the Baltic and the Black Sea are testimony to the rising waters that swallowed them.

Underwater cultural heritage can reveal aspects of history that are not yet known or that have not been accounted for in written records. For instance, the ancient trade between China and Africa, Indonesia and Australia, as well as the sophistication of ancient indigenous people can now be proven due to artefacts discovered on the seabed or in submerged caves. Since water has been used since the beginning of civilization as a way to connect different worlds, the remains to be found on seabeds are testimony to cultural dialogue from the beginning of humankind.

Many of these sites have remained untouched over centuries or even millennia. The biological material that they contain is therefore often much better preserved than on land, due to the lack of oxygen, which would have facilitated its deterioration. This makes these sites unique. For this same reason, in situ protection of these sites is a first priority.

Preservation facilitates the economic benefits that underwater cultural heritage sites can generate. Diving tourism and maritime museums can be a significant economical attraction for an area or a city. It is not only their entrance fees that can be quite substantial, even more important is the economic impact they have on the cultural tourism industry and local tourist accommodation.