Recreational scuba diving can affect the underwater environment, especially in places where many divers visit. These areas often show signs of harm caused by divers who are not properly trained for the local conditions, do not receive enough information before diving, or do not understand how to protect marine life and ecosystems. However, diving can also have some positive effects. Local communities may value the environment more when it is healthy, leading to support for conservation efforts. Some divers help monitor coral reefs by collecting data for scientists, which can improve environmental protection over time.

In the 20th century, recreational scuba diving was seen as having little environmental impact, so it was allowed in many marine protected areas. Since the 1970s, diving has become more popular and accessible to a wider group of people. Better equipment and shorter training requirements have made diving easier, but less focus has been placed on protecting the environment. As more people dive and visit sensitive underwater areas, the need to manage the activity’s impact on ecosystems has become clear.

Scuba diving has grown in popularity during the 21st century, with about 23 million certifications worldwide by 2016. Scuba diving tourism is a growing industry, and it is important to consider how it affects the environment. Divers can harm marine life in different ways, depending on the environment. Tropical coral reefs are more easily damaged than temperate reefs, which are stronger and more resilient. The same conditions that make these areas attractive to tourists also make them more vulnerable to harm from untrained divers. Efforts are being made to balance conservation with the needs of the diving industry.

Avoiding contact with sea life on the ocean floor requires motivation and proper training. Training that teaches low-impact diving has been shown to help divers avoid harming the environment when they are motivated. A diver’s experience, attitude toward diving and the environment, and personality type are important factors in how they behave underwater.

Affected environments

All underwater areas visited by recreational divers may be affected, but the effects are more noticeable in places with many dives or environments that have delicate, slow-growing life or fragile structures. Examples include tropical coral reefs and flooded caves with fragile speleothems. Many studies have focused on tropical coral reefs because they face the highest pressure from human activity. Coral reefs can repair themselves to some degree and also suffer damage from natural causes, so a level of ongoing damage from divers might be acceptable if it matches the reefs' natural ability to recover. Underwater speleothems, however, do not regrow once broken while the cave remains flooded, and the damage would last forever if measured by human timescales. Underwater cultural heritage, such as historically important shipwrecks and archaeological sites, can also be damaged in ways that cannot be fixed, though these sites naturally decline over time regardless of diving activity. Diver activity mainly speeds up this natural decline.

Subtropical, temperate, and polar marine reef environments differ in how well they can recover from harm. These areas were historically thought to be less affected by diving, so fewer studies have been done on diver damage, reef recovery, and how many divers can be supported without harm. These regions are now becoming more popular for diving, and research about how diving affects their environments is increasing.

Types of impact

Studies show that diving can harm tropical coral reefs. Areas with heavy diving often have less coral and changes in coral shape, with stronger corals becoming more common and fewer types of coral over time. These reefs may be more likely to suffer from other problems, such as disease or storm damage.

There is strong evidence that poorly planned or too much tourist activity can damage reefs and reduce the enjoyment of diving areas. Marine tourism harms reefs directly through actions like breaking coral, boats hitting reefs, and anchors damaging the seafloor. It also harms reefs indirectly by making water quality worse through pollution, waste, and cloudy water. How much damage happens depends on how often, how long, and how intensely people use the area, as well as the environment.

Divers can harm corals by breaking their skeletons, scraping their surfaces, which may cause disease, and reducing the amount of hard coral on reefs. Diving activities can also make reefs less able to handle stress from events like climate change and coral bleaching.

In some tropical coral reef areas, recreational divers have caused harm by accidentally touching live corals, damaging them faster than the reefs can recover naturally. Over time, this leads to reef damage. A major challenge for local leaders is finding ways to enjoy tourism while protecting reefs for the future.

In "muck diving" areas with soft sediment, taking photos causes more environmental harm than factors like diver experience, age, or gender. Divers touch the seafloor more often in soft sediment than on coral reefs, but the damage is not worse. Divers also touch animals more when photographing small sea creatures and spend more time interacting with them when using heavy cameras. Long-term effects of this behavior on these animals and soft sediment areas are not known.

Studies looked at how photographers and camera flashes affect small sea creatures. Results showed little harm beyond what happens when people are simply present. Camera flashes did not harm seahorses' eyes or affect their ability to eat. Handling animals directly caused them to become very stressed.

Less research has been done on how diving affects subtropical and temperate reefs compared to tropical reefs. Some people think these reefs are less likely to be harmed because their fixed sea creatures are less exposed to divers. Studies in the Mediterranean show that certain fragile sea creatures with brittle skeletons are not able to recover from repeated disturbances by divers.

Divers often touch the seafloor in temperate reefs, freshwater areas, and caves. One common issue is divers' fins stirring up sediment, making water cloudy and reducing visibility. Moving sediment and delicate sea life without direct contact is also a concern.

Recreational scuba diving can harm dive experiences and damage shipwrecks, which are cultural treasures. Four main types of damage have been found:
• Taking items from wreck sites and disturbing them,
• Divers and their equipment touching wrecks and the sea life living on them,
• Air bubbles from divers getting trapped inside wrecked ships,
• Damage from boat anchors, which some researchers say is the most harmful type of damage. Anchors can break fragile wreckage, but lighter weights used for securing ropes usually cause less damage. This damage can be avoided by using permanent anchors at popular wreck sites.

Studies about how often men and women harm reefs have not reached clear conclusions. Different research has given conflicting results.

Reasons for impact

Repetitive contact between divers, their equipment, and the underwater environment is a common way recreational diving harms coral reefs. Factors that increase the chance of reef contact include:

• Time since the last dive – Longer intervals between dives are linked to worse buoyancy control and less skill.
• Number of dives completed – Fewer dives are connected to worse buoyancy control and less skill.
• Where divers received training – Training in simple conditions does not teach advanced skills, but experience in similar environments helps divers recognize delicate organisms.
• Awareness of marine park rules.
• Use of cameras – Photographers are more likely to touch the reef when focused on taking pictures.
• Dive depth – Divers make fewer contacts at greater depths, though the reasons are not fully understood.
• Large groups of divers – More impacts occur early in dives when divers are adjusting their buoyancy and learning the environment, especially if entry points are near shallow coral or if divers are unfamiliar with the area.

Experience does not always predict how often divers touch the reef, but training in low-impact skills reduces contact for all divers, regardless of experience. Fin movements cause the most damage to reef life, especially branching corals, which are more vulnerable. Reducing damage requires better buoyancy, fin techniques, awareness of the reef's location, and understanding how close proximity to sensitive organisms can harm them. Training in these skills helps divers avoid contact with the reef.

Site shape does not strongly affect coral damage, but coral type and strength do. Branching corals, which are weaker, suffer the most damage. Studies show that poor buoyancy control is the main reason inexperienced divers touch the reef. Divers who cannot maintain neutral buoyancy (staying at a steady depth) are more likely to contact the reef. Teaching divers about the harm of reef contact helps those with good buoyancy skills, but not those without the skill. The solution is ensuring divers have the necessary skill before diving in sensitive areas.

Dive guides may find it harder to influence larger groups of divers, but programs focusing on industry practices can reduce human-caused reef damage. Some marine protected areas in the Mediterranean have banned scuba diving or limited it to areas near the edges of protected zones. Others created diving trails to avoid vulnerable spots. Conservation efforts also identify sensitive species and set limits on visitor numbers based on their needs.

A 2012 study in Malaysia found that experience is the most important factor in how divers behave underwater, followed by their attitudes toward diving and personality. Awareness of environmental protection helps connect experience to behavior, but another study found that understanding the importance of protecting the environment has a stronger effect than skill alone on motivating divers to avoid harming reefs. Avoiding reef contact needs both motivation and the right skills.

Strategies for reducing diver impact

Correct weighting is an important step for good buoyancy control. Good buoyancy control is needed (but not enough) to keep the body level in the water. Keeping the body level helps keep fins higher above the seafloor on most reefs, which reduces how often the fins touch the reef and disturb the sand. Removing or shortening loose equipment lowers the chance that items will hit the reef when the diver is near it. Being aware of how close the diver is to the environment helps avoid movements that could cause the diver to touch the reef, especially in ways that cause damage. Using proper kicking techniques can reduce the chance of hitting the reef. For example, vertical kicking in flutter kicks is more likely to hit the reef below the diver, while side-to-side kicking in frog kicks is more likely to hit a reef wall. Understanding how reef contact affects marine life and knowing which local species are most vulnerable helps divers avoid harming those organisms. This knowledge may also encourage divers to take more care to avoid contact. Adjusting how close the diver is to the seafloor based on sea conditions can help manage the risk of contact when waves or currents change.

Entry-level diver training focuses on keeping divers safe. These programs are usually as short as allowed by standards and only briefly mention how divers can affect the underwater environment and ways to reduce that impact. There is rarely any training beyond basic survival skills and buoyancy control. Divers receive certification for meeting the minimum safety requirements, but some may not even meet those standards. Information about how divers affect the environment is not considered critical for safety, so it is often not tested or considered when evaluating a diver's skills, even if it could be helpful. Most recreational divers do not take further training and may only dive occasionally, so they may forget skills faster than they learn them. Refresher courses to review basic safety skills are common. Basic training alone cannot ensure diving with minimal impact, especially in areas that are very different from where the training was done. The amount and quality of information about environmental impact in entry-level training materials also vary between training providers.

Several studies show that much of the damage to underwater environments could be avoided if divers change their behavior through education and in-water demonstrations. Short pre-dive briefings alone do not significantly reduce contact with the reef.

In 2012, Camp and Fraser found that divers who took environmental conservation courses had similar reef contact rates as those who did not. However, conservation education given during a dive briefing reduced reef contact, and the depth of that education affected how well it worked. Divers who knew the local environment better also had fewer impacts.

Some scuba diving programs teach not only proper techniques and equipment use but also focus on protecting the environment, especially coral reefs. For example, in the Florida Keys, companies offer advanced open-water training that teaches divers about the effects of recreational diving on ocean wildlife. These programs also partner with groups like the Blue Star Dive Center and the Coral Restoration Foundation to emphasize keeping a safe distance from sea life to protect the underwater environment.

Low-impact diving training has been shown to reduce the number of times divers touch the reef.

In 1989, Buoyancy Training Systems International, a company in Seattle, Washington, created the first worldwide training program and underwater test to reduce diver impact on marine life. The program, now called the Diamond Reef System, uses portable reef simulation structures called "Diamond Reef Hover Stations" to help divers at all skill levels improve their abilities and awareness. This program is still used globally by dive operators and the U.S. Environmental Protection Agency.

The PADI Low Impact Diver program takes two days and works well for divers with different skill levels. Similar programs from other providers likely have similar results. Many of these skills are also taught in technical diving, such as cave and wreck diving, where they are important for safety.

While training and experience are essential for low-impact diving, a diver's attitude toward the environment and personality may influence how they use their skills to reduce harm to marine life.

Strategies for sustainable use management

Several methods have been created to help reduce the harm that divers can cause to coral reefs.

Carrying Capacity Approach: This method limits the number of divers allowed in an area. However, this can also reduce the money earned from tourism. The number of divers that can safely visit a site depends on many factors. These include the shape of the coral, the presence of animals that are easily harmed, how well divers understand and protect the environment, other problems that affect the reef, the size of the reef, the shape of the reef, and the weather conditions in the water. Adjustments may need to be made often to account for changes, unknowns, and mistakes in models.

Limits of Acceptable Change: This method uses numbers to set limits on how much a reef can change based on goals for protecting the area. It works poorly if natural changes are not known, and it cannot tell if changes are caused by diving or other factors. In some cases, there may not be a clear example of what the reef looked like before any damage happened.

Percentile Approach: This method compares the damage to coral at places where divers are active with similar places where no diving happens. If the average damage at a diving site reaches or exceeds the level of damage found in 80% of the comparison sites, action is taken. This method has problems if the comparison sites are already damaged, if damage from non-divers is mistaken for damage from divers, or if the comparison sites have unusual conditions.

Limiting Divers to Specific Areas: This method keeps divers in certain parts of the reef. This often causes damage to be concentrated along paths where divers travel, harming the reef and making visitors unhappy as the paths become worse over time.

Regulating Diving Equipment: This method restricts the use of items like gloves and cameras, which can increase contact with the reef. These rules are often disliked by photographers and may affect both skilled and unskilled divers. The cost and complexity of equipment do not always match a diver’s skill level.

Changing How Services Are Provided: More supervision by dive guides can help reduce damage if divers are skilled enough to follow instructions. However, this does not fix basic skill problems, which are common. Briefings before diving can help reduce damage if divers are skilled enough to avoid harm. Experience is not always a sign of skill, but lack of experience or infrequent practice often means poor buoyancy and movement skills. Better results happen when there are fewer divers for each guide.

The number of dives that can happen without harming the reef depends on many factors. These include the presence of animals that are easily harmed, the skill and awareness of divers, water conditions like currents and waves, human-related stressors, the shape of the reef, and the size of the area. Regular checks are needed even if no major changes happen. Conditions can vary greatly even within the same area. For example, a tropical reef with branching coral near a calm area may have different needs than a rocky reef near a busy city with strong waves and seasonal changes. The right equipment and skills also vary, and unfamiliar gear may take time to learn. Training divers should not be allowed in popular areas where many visitors dive. Service providers must ensure that diving does not harm coral reefs, and researchers should study the actual effects of diving in busy areas.

Some diving activities can help the environment. These include volunteers monitoring reefs, photographers reporting what they see, tourists encouraging conservation, and divers cleaning up trash. Most volunteer projects need long-term commitment and training, making them better suited for local people than tourists.

Marine Conservation Projects Using Volunteer Divers:
– Coral Reef Alliance: A group that protects coral reefs.
– Green Fins: A charity that helps save coral reefs.
– Project AWARE: An international group that works on environmental issues.
– Reef Check: A group focused on protecting coral reefs.
– Reef Life Survey: A program that monitors marine life in Tasmania.

Databases for Observing Nature:
– iNaturalist: A website and app for sharing observations of plants and animals.
– iSpot: A website where people can share information about wildlife.

Specific regions of study

• Eastern Australia
• Kish Island, Iran (Persian Gulf)
• Hong Kong, China
• Great Barrier Reef, Australia
• Indonesia
• Malaysia
• New South Wales, Australia
• Okinawa, Japan
• Persian Gulf
• Philippines
• Red Sea
• Sierra Helada Marine Park, Spain (Mediterranean Sea)
• Silfra, Iceland
• Sodwana Bay, South Africa
• Southern Mozambique
• Table Mountain National Park Marine Protected Area, South Africa.