Cross-sea bridges are bridges that cross bays, straits, deep waters, inlets or other marine waters, and generally have long spans and lines, ranging from a few kilometres to several tens of kilometres.Some bridges are long and often consist of several bridges within bridges; to avoid affecting waterways or air routes, a part of the bridge may also be a subsea tunnel, combining 'bridge, island and tunnel'.

In the marine environment, bridges are subjected to the interaction of a variety of corrosion factors, and even extreme weather conditions such as typhoons and thunderstorms, which can damage the structural integrity and stability of the bridge. Therefore bridge corrosion protection technology and corrosion protection management are extremely important to the construction of cross-sea bridges.

The Seto Bridge in Japan is a bridge across the Seto Inland Sea between Honshu (Kurashiki City, Okayama Prefecture) and Shikoku (Sakaida City, Kagawa Prefecture), and is one of three routes in the Honshu-Shikoku Link Bridge network. The bridge is connected by several suspension bridges, inclined tension bridges and girder bridges, forming a spectacular bridge complex. Construction began on 10 October 1978 and took nearly 10 years to complete, with the 37.3km bridge opening on 10 April 1988.

The Chesapeake Bay Bridge is a two-way transoceanic bridge that runs from Norfolk to the Delaware Peninsula, creating a water promenade between the Chesapeake Bay and the Atlantic Ocean. Located between Maryland and Virginia, the 37 km long Chesapeake Bay Bridge was completed and opened in 1964, when it was called one of the Seven Wonders of the Modern World.

The King Fahd Bridge, also known as the Bahrain Causeway Bridge, is located in the Gulf of Bahrain in the Persian Gulf and is a cross-sea road bridge between Bahrain and Saudi Arabia. The bridge runs from Jasra in the west of the island to Al-Azizia in Saudi Arabia and is 25 kilometres long, with 10 kilometres of reclaimed embankment and 15 kilometres of bridges, connected by five bridges.

The Hong Kong-Zhuhai-Macao Bridge (HZMB) is a bridge-tunnel project in China linking Hong Kong, Guangdong Province and Macau. It is located in the Lingdingyang area at the mouth of the Pearl River in Guangdong Province, and is world-renowned for its sheer scale of construction unprecedented difficulty of construction and state-of-the-art technology. The Hong Kong-Zhuhai-Macao Bridge is 55 kilometres long, including 29.6 kilometres of the main bridge and 41.6 kilometres from the China Hong Kong Crossing to the Zhuhai-Macao Crossing; the bridge is a two-way six-lane motorway with a design speed of 100 km/h. It has a design life of 120 years and is capable of resisting earthquakes of magnitude 8 and typhoons of magnitude 16.