Underwater diving
Environmental impact

The environmental impact of recreational diving is the effects of diving tourism on the marine environment. Usually these are considered to be adverse effects, and include damage to reef organisms by incompetent and ignorant divers, but there may also be positive effects as the environment is recognised by the local communities to be worth more in good condition than degraded by inappropriate use, which encourages conservation efforts. During the 20th century recreational scuba diving was considered to have generally low environmental impact, and was consequently one of the activities permitted in most marine protected areas. Since the 1970s diving has changed from an elite activity to a more accessible recreation, marketed to a very wide demographic. To some extent better equipment has been substituted for more rigorous training, and the reduction in perceived risk has shortened minimum training requirements by several training agencies. Training has concentrated on an acceptable risk to the diver, and paid less attention to the environment. The increase in the popularity of diving and in tourist access to sensitive ecological systems has led to the recognition that the activity can have significant environmental consequences.

Recreational scuba diving has grown in popularity during the 21st century, as is shown by the number of certifications issued worldwide, which has increased to about 23 million by 2016 at about one million per year. Scuba diving tourism is a growth industry, and it is necessary to consider environmental sustainability, as the expanding impact of divers can adversely affect the marine environment in several ways, and the impact also depends on the specific environment. Tropical coral reefs are more easily damaged by poor diving skills than some temperate reefs, where the environment is more robust due to rougher sea conditions and fewer fragile, slow-growing organisms. The same pleasant sea conditions that allow development of relatively delicate and highly diverse ecologies also attract the greatest number of tourists, including divers who dive infrequently, exclusively on vacation and never fully develop the skills to dive in an environmentally friendly way. Low impact diving training has been shown to be effective in reducing diver contact.

The ecological impact of commercial diving is a small part of the impact of the specific industry supported by the diving operations, as commercial diving is not done in isolation. In most cases the impact of diving operations is insignificant in comparison with the overall project, and environmental impact assessments may be required before the project is authorised for some classes of project. Underwater ships husbandry may be an exception to this general tendency, and specific precautions to limit ecological impact may be required. Several of these operations will release some quantity of harmful material into the water, particularly hull cleaning operations which will release antifouling toxins. Alien biofouling organisms may also be released during this process. Other forms of professional diving, such as scientific and archaeological dives, are planned to minimise impact, which may be a condition for the application for a permit.
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