Sometimes, entire villages are submerged under the waters of a reservoir.
When the level of waters is low, the structures can emerge and be visible.
[2] An ancient forest stood in the area between Bray, County Wicklow and Killiney before being submerged by rising sea levels c. 4000 BC.
Under the Irish Sea is a "prehistoric palaeolandscape of plains, hills, marshlands and river valleys, in which evidence of human activity is expected to be preserved"; it has been compared to Doggerland in the North Sea.
[2] Other submerged sites, according to the National Monuments Service, include "landscapes, harbours, jetties, landing places, fish traps, kelp grids, bridge sites, crannogs and tidal mills.