Underwater archaeology deals with archaeological sites found below the surface of oceans, rivers, and lakes and on the foreshore. In addition to shipwrecks, underwater archaeologists study submerged aboriginal sites such as fish weirs and middens; remains of historic structures such as wharves, canal locks, and marine railways; sunken aircraft; and other submerged cultural heritage resources.
Underwater archaeology shares the same methodology and principles as archaeology carried out on land sites. All archaeology involves the careful study of artefacts, structures and features to reconstruct and explain the lives of people in the past. However, because it is carried out in a more challenging environment, underwater archaeological fieldwork is more complex than land archaeology.
Specialized techniques and equipment are required to work productively underwater. Staying warm during long dives is a constant concern, so underwater archaeologists often use masks that cover their entire faces, dry suits worn over layers of warm clothing, or in cases where the water is extremely cold, such as the excavation in Red Bay (Labrador), wet suits supplied with a flow of hot water. Underwater communication systems are used to talk to people on the surface or to other divers. Removing sediments covering underwater sites requires the controlled use of specially designed equipment such as suction airlifts and small dredges. Recording information underwater presents its own challenges. Special underwater paper is used for notes and drawings, while photo and video cameras are placed in waterproof housings.
Underwater archaeological fieldwork includes remote-sensing surveys using geophysical techniques, diving surveys to locate and map sites, site monitoring, and excavation. The success of an underwater archaeological project rests on accurate documentation of all aspects of the process. Meticulous mapping and recording are particularly essential when excavation is required, as artefacts and other physical evidence are permanently removed from their original contexts. Archaeologists aim to be able to reconstruct the entire site from the records they generate during fieldwork.