An underwater survey is a survey performed in an underwater environment or conducted remotely on an underwater object or region. Survey can have several meanings. The word originates in Medieval Latin with meanings of looking over and detailed study of a subject. One meaning is the accurate measurement of a geographical region, usually with the intention of plotting the positions of features as a scale map of the region. This meaning is often used in scientific contexts, and also in civil engineering and mineral extraction. Another meaning, often used in a civil, structural, or marine engineering context, is the inspection of a structure or vessel to compare actual condition with the specified nominal condition, usually with the purpose of reporting on the actual condition and compliance with, or deviations from, the nominal condition, for quality control, damage assessment, valuation, insurance, maintenance, and similar purposes. In other contexts it can mean inspection of a region to establish presence and distribution of specified content, such as living organisms, either to establish a baseline, or to compare with a baseline.

Underwater construction is industrial construction in an underwater environment. It is a part of the marine construction industry. It can involve the use of a variety of building materials, mainly concrete and steel. There is often, but not necessarily, a significant component of commercial diving involved. Some underwater work can be done by divers, but they are limited by depth and site conditions, and it is hazardous work, with expensive risk reduction and mitigation, and a limited range of suitable equipment. Remotely operated underwater vehicles are an alternative for some classes of work, but are also limited and expensive. When reasonably practicable, the bulk of the work is done out of the water, with underwater work restricted to installation, modification and repair, and inspection.