Underwater structures are man-made constructions located beneath the surface of water bodies, such as oceans, rivers, and lakes. These structures can include bridges, tunnels, oil rigs, and submarine cables, designed to support various activities like transportation, energy production, and communication. These structures are engineered to withstand harsh underwater conditions, including pressure, corrosion, and marine life. They often require specialized materials and construction techniques to ensure durability and safety. Examples of underwater structures include the Channel Tunnel connecting England and France and offshore wind farms that harness renewable energy.