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Diver at the wreck of the Hilma Hooker, Netherlands Antilles.

Wreck diving is a type of recreational diving where shipwrecks are explored. Although most wreck dive sites are at shipwrecks, there is an increasing trend to scuttle retired ships to create artificial dive sites. Shipwreck diving enables sport divers to visit the past. Each wreck is considered a time capsule into history waiting to be explored. Sport divers also make interesting artifact finds while exploring the remains of sunken ships. This enables the sport diving community to make its own contribution to historians and archaeologists by giving them the information needed for wreck identification and further research.

A shipwreck is attractive to divers for several reasons:

• it is an artificial reef, which creates a habitat for many types of marine life
• it often is a large structure with many interesting parts and machinery, which is not normally closely observable on working, floating vessels
• it often has an exciting or tragic history
• it presents new skill challenges for scuba divers
• it is part of the underwater cultural heritage and may be an important archaeological resource
• it provides a first-hand insight into context for the loss, such as causal connections, geographical associations, trade patterns and many other areas, providing a microcosm of our maritime heritage and maritime history.

Wrecks may pose a variety of unique hazards to divers. Wrecks are often snagged by fishing lines or nets and the structure may be fragile and break without notice. Penetration diving, where the diver enters a shipwreck is an advanced skill requiring special training and equipment. Many attractive or well preserved wrecks are in deeper water requiring deep diving precautions. It is advisable to have a pair of shears or a diving knife which could be used in the event that the diver is entangled with fishing lines or ropes and to have a spare light source in case the primary light fails. If penetrating a wreck, a guideline tied off before entering a wreck and run out inside the wreck is advisable. A guideline helps a wreck diver in finding the way out easier in case of low visibility due to stirred up sediments. For penetration diving, a greater reserve of breathing gas should be allowed for, to ensure there is sufficient to get out of the wreck. Most wreck divers use a minimum of the rule-of-thirds for gas management. This allows for 1/3 of the gas down and into the wreck, 1/3 for exit and ascent and 1/3 reserve. In addition, because of the potential fragility of the wreck, the likelihood of disturbing sediments or disturbing the many marine animals that take advantage of the artificial habitat offered by the wreck, extra care is required when moving and finning.

Diver with porthole recovered from a shipwreck in New York's Wreck Valley: Shipwreck Expo

Many diver training organizations provide specialist wreck diver training courses, such as SDI, and PADI Wreck Diver, which divers are advised to take before wreck diving. Such courses typically teach skills such as air management and the proper use of guidelines and reels. Other organizations, such as IANTD and TDI teach advanced wreck courses, that emphasize a high level of training, experience and equipment . The Nautical Archaeology Society in the UK, teaches awareness of underwater cultural heritage issues as well as practical diver and archaeological skills. Other organizations, such as the Artificial Reef Society of British Columbia (ARSBC) deliberately create artificial reefs to provide features for divers to explore, as well as substrates for marine life to thrive upon.

A notice proclaiming the protected status of HMS Hazardous near Portsmouth, England

In many countries, wrecks are legally protected from unauthorized salvage or desecration.

In the United Kingdom, three Acts protect wrecks:

• Protection of Wrecks Act 1973 : certain designated, charted, historic or dangerous sites may not be dived without a license
• Protection of Military Remains Act 1986 : all military aircraft and 16 designated ships are considered war graves that can only be dived with a license. Other non-designated ships may be dived providing the divers do not enter, disturb or remove artifacts
• Merchant Shipping Act 1995 : all wrecks and cargoes are owned: each artifact removed must be reported to the Receiver of Wreck

Wrecks that are protected are denoted as such on nautical charts (such as admiralty charts); any diving restrictions should be adhered to.

• Further information on Wreck Diving Specifics

• Shipwrecks
• Archaeology of shipwrecks
• Aviation archaeology
• Nautical Archaeology Society
• Marine salvage
• Diver training