Recreational dive sites

Sea and ocean shorelines, reefs and shoals are salt water sites and may support high biodiversity of life forms. Tropical coral reefs are the most popular diving tourism destinations. Rocky reefs are more widespread, and support a greater variety of ecosystems, though the local biodiversity is usually more limited. Shipwrecks are also common on some coasts, and are very popular attractions for a large number of divers. Unconsolidated sediment is less likely to be visited intentionally, though there are some muck diving sites known for interesting animals.

Lakes usually contain fresh water. Large lakes have many features of seas including wrecks and a variety of aquatic life. Depths may vary considerably, though they are shallow compared to the open ocean, and while surface water level may vary over the long term, they do not have noticeable tides, and seldom have significant currents. Some lakes are at high altitude and may require special considerations for altitude diving.

Artificial lakes, such as clay pits, gravel pits, quarries and dams often have low visibility. Flooded quarries are popular in inland areas for diver training and sometimes also recreational diving. Rock quarries may have reasonable underwater visibility if there is not so much mud or silt to cause low visibility. As they are not entirely natural environments and usually privately owned, quarries often contain features intentionally placed for divers to explore, such as sunken boats, automobiles, aircraft, and abandoned machinery and structures. Flooded mines may provide the equivalent of flooded caves with an overhead environment, though generally with a known extent.

Rivers generally contain fresh water but are often shallow and turbid and may have strong currents.

Caves containing water provide exotic and interesting, though relatively hazardous, opportunities for exploration, and are found both inland and at the coast of the sea.

Divers may choose to get into the water to explore any arbitrary place where conditions appear to be good enough to justify the effort, but do not necessarily record what is there, or even that the site exists, but a popular recreational dive site will usually be named, and a geographical position identified and recorded, describing the site with enough accuracy to recognise it, and hopefully, find it again.

Names for the sites themselves range from descriptive through quixotic to pretentious, as they are chosen at the whim of whoever dives there and names the site. There is often no standardisation, and the same site may be known by different names to different divers. Few sites are reliably mapped or have a published description with an accurate position, and many of these are caves or wrecks of identified ships. It is also common for a dive site to be named after a charted feature, such as a reef, exposed rock, promontory, or other navigational landmark, and like landmarks, the same name may be used for more than one dive site. Other sites are named for ecological features, like a species common at the site, or one that was seen there on an exploration dive. Sites that are frequently used by commercial service providers may be given names which are intended to promote the site to potential customers.

NASA image showing locations of significant coral reefs, which are often sought out by divers for their abundant, diverse life forms.

There are a wide range of underwater features which may contribute to the popularity of a dive site:

• Accessibility is important, but not critical. Some divers will travel long distances at considerable cost to get to a site with exceptional features.
• Biodiversity at the site: Popular examples are coral, sponges, fish, sting rays, molluscs, cetaceans, seals, sharks and crustaceans. Colourful organisms generally increase popularity of a site.
• The topography of the site: Coral reefs, walls (underwater cliffs), rocky reefs, gullies, caves, overhangs and swim-throughs (short tunnels or arches) can be spectacular. Terminology for the topography of dive sites is generally consistent with oceanographic practice, with occasional more eccentric usage.
• Historical or cultural items at the site: Shipwrecks, sunken aircraft and archaeological sites, apart from their historical value, form artificial habitats for marine life making them more attractive as dive sites.
• Underwater visibility: This can vary widely between sites and with time and other conditions. Poor visibility is caused by suspended particles in the water, such as mud, silt, suspended organic matter and plankton. Currents and surge can stir up the particles. Rainfall runoff can carry particulate matter from the shore. Diving close to the sediments on the bottom can result in the particles being kicked up by the divers fins. Sites which generally have good visibility are preferred, but poor visibility will often be tolerated if the site is sufficiently attractive for other reasons.
• Water temperature: Warm water diving is comfortable and convenient, and requires less equipment. Although cold water is uncomfortable and can cause hypothermia, cold water sites can be interesting because different species of underwater life thrive in cold conditions, and many interesting wrecks, caves and other features happen to be in cold water.
• Currents and tidal flows can transport nutrients to underwater environments increasing the variety and biomass of life at a site. Currents can also be dangerous to divers as they can carry the diver away from the surface support or the planned exit point. Currents that flow over large obstructions can cause strong local vertical currents and turbulence that are dangerous because they may cause the diver to lose buoyancy control risking barotrauma, or impact against the bottom terrain.

Sites are generally rated for quality by people who do not have an exhaustive experience of the full range of sites throughout the world, and preferences differ. Criteria used for rating may differ, and are seldom specified. It is unlikely that any published ratings are unbiased, and they are not usually accompanied by a conflict of interest disclaimer. Conditions at most sites vary from day to day, often considerably, depending on various factors, particularly recent weather. The quality of the diving experience will also vary depending on the conditions at the time.

Recreational dive sites of the greater Cape Town region. The yellow lines indicate the boundary of the Table Mountain National Park MPA.

Marine bioregions of the South African coast

The Table Mountain National Park Marine Protected Area around the Cape Peninsula is a popular diving region in the Atlantic Ocean, in the vicinity of Cape Town, South Africa, with more than 250 named dive sites, many of which have been surveyed and mapped. The Cape Peninsula marks the boundary between the cool temperate Benguela ecoregion, which extends from Namibia to Cape Point, and is dominated by the cold Benguela Current, and the warm temperate Agulhas ecoregion to the east of Cape Point which extends eastwards to the Mbashe River. The break at Cape Point is very distinct in the inshore depth ranges, and the waters of the east and west sides of the peninsula support noticeably different ecologies, though there is a significant overlap of resident organisms. There are a large proportion of species endemic to South Africa along this coastline.[10][11][12]

The Tsitsikamma Marine Protected Area in the south coast of South Africa is another temperate region of high biodiversity and endemism, but the tourism infrastructure is not optimised for diving, as the sea conditions are somewhat unpredictable.

• Great Barrier Reef
• Indonesia
• The Red Sea
• Caribbean Sea
• The iSimangaliso Marine Protected Area is a coastal and offshore marine protected area in KwaZulu-Natal from the South Africa-Mozambique border in the north to Cape St Lucia lighthouse in the south.[13] There is a diving resort area serving this MPA at Sodwana Bay. The recreational diving area is in the tropical Delagoa ecoregion in the north of kwaZulu-Natal, which extends from Cape Vidal northwards into Mozambique. There are some species endemic to South Africa along this coastline, but most of the species are tropical Indo-Pacific.[12] This is one of the very few places that coelacanths have been seen in their natural habitat by divers.

Wreck diving is recreational diving where the wreckage of ships, aircraft and other artificial structures is visited. Although most wreck dive sites are the remains of ships sunk by accident or enemy action in times of war, there are a large number of ships scuttled to create dive sites at places where the conditions are more suitable for recreational diving. The recreation of wreck diving makes no distinction as to how the vessel ended up on the bottom, though this may be of importance to the individual diver, and some wreck hunters spend large amount of time and money in searches for unlocated wrecks. There is a large overlap between recreational and archaeological wreck hunting and diving, and in some cases between recreational wreck diving and unauthorised recovery of artifacts. Some wreck diving involves penetration of the wreckage, making a direct ascent to the surface impossible for a part of the dive. Only a small fraction of the world's shipwrecks are in known positions suitable for access by divers, and their condition deteriorates over time.

Coral reef areas

Rocky reefs

Cave diving is underwater diving in water-filled caves. It may be considered an extreme sport due to the range of hazards and the difficulty of mitigating them to an acceptable level. The equipment used varies depending on the circumstances, and ranges from breath hold to surface supplied, but almost all cave diving is done using scuba equipment, often in specialised configurations. Recreational cave diving is generally considered to be a type of technical diving due to the lack of a free surface during large parts of the dive, and often involves decompression.

A distinction is made by recreational diver training agencies between cave diving and cavern diving, where cavern diving is deemed to be diving in those parts of a cave where the exit to open water can be seen by natural light. An arbitrary distance limit to the open water surface may also be specified.[14] There are relatively few practitioners of cave diving. This is due in part to the specialized equipment and skill sets required, and in part because of the high potential risks due to the specific environment. Despite these risks, water-filled caves attract scuba divers, cavers, and speleologists due to their often unexplored nature, and present divers with a technical diving challenge. Underwater caves have a wide range of physical features, and can contain fauna not found elsewhere.

Constructing an artificial reef using concrete breeze blocks[15]

An artificial reef is a human-created underwater structure, typically built to promote marine life in areas with a generally featureless bottom, to control erosion, block ship passage, block the use of trawling nets,[16] or improve surfing.

Many reefs are built using objects that were built for other purposes, such as by sinking oil rigs (through the Rigs-to-Reefs program), scuttling ships, or by deploying rubble or construction debris. Other artificial reefs are purpose-built (e.g. the reef balls) from PVC or concrete. Shipwrecks may become artificial reefs when preserved on the seafloor. Jetties and breakwaters are secondarily artificial reefs. Regardless of construction method, artificial reefs generally provide hard surfaces where algae and sessile ebibenthic invertebrates such as barnacles, corals, and oysters attach; the accumulation of attached marine life in turn provides intricate habitat and food for mobile benthic invertebrates and assemblages of fish.

Occasionally sculpture works have been placed underwater singly or in groups, as attractions for divers, and they also function as artificial reefs.[17][18][19][20]

Wazee Lake near Black River Falls, Wisconsin is a former iron mining quarry now used for scuba diving and other uses.

Scuba diving quarries are depleted or abandoned rock quarries that have been allowed to fill with ground water, and rededicated to the purpose of scuba diving. They may offer deep, clean, clear, still, fresh water with excellent visibility, or low visibility in turbid water from surface runoff. They have no currents or undertow. They are often used as training sites for new divers, where classes and certification dives are carried out. Many have a dive shop on site to rent out equipment and sell air fills and diving equipment. Lodging or camping areas may be available on site.

Quarries in stone may have clear water, with greater visibility than in many inland lakes. Ground water is the primary source of the water that fills these quarries once they are no longer pumped out for mining operations. Many quarry mining operations are located in areas where filling from other, less clean sources, such as rivers and surface runoff of rainwater is not as likely.

Over time, most quarries tend to be contaminated with erosion products and nutrients from surface runoff, causing many to develop a green tint due to algae growth, and accumulations of silt on the bottoms and other surfaces.

Fresh water scuba diving does not require much difference in equipment from diving in the sea. Water temperatures generally decrease as depth increases, and may be as low as 4 °C (39 °F) at depth. In those temperatures dry suit diving is recommended, but in warmer temperatures, wetsuits may be sufficient. Diving in clean fresh water generally requires less post dive maintenance.

The operators of scuba diving quarries may add objects or debris fields to the bottom of the quarry for divers to explore while scuba diving. Mostly these are man made objects such as boats, cars, and trucks. Some quarries have such large objects as school buses, small buildings, or commercial airliners on the bottom. These sites may be mapped out and marked with guide lines under the water, particularly if visibility is poor.

The owners or operators of quarries may stock the quarry with fish to provide entertainment for divers. These are commonly the same species of fish that thrive naturally in local lakes and rivers, but some quarries are stocked with more exotic fish. The ecology is usually very limited.