The environmental impact of recreational diving is the effects of recreational scuba diving on the underwater environment, which is largely the effects of diving tourism on the marine environment. It is not uncommon for highly trafficked dive destinations to have more adverse effects with visible signs of diving's negative impacts due in large part to divers who have not been trained to sufficient competence in the skills required for the local environment, an inadequate pre-dive orientation, or lack of a basic understanding of biodiversity and the delicate balance of aquatic ecosystems. There may also be indirect positive effects as the environment is recognised by the local communities to be worth more in good condition than degraded by inappropriate use, and conservation efforts get support from dive communities who promote environmental awareness, and teach low impact diving and the importance of respecting marine life. There are also global coral reef monitoring networks in place which include local volunteer divers assisting in the collection of data for scientific monitoring of coral reef systems, which may eventually have a net positive impact on the environment.

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.

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. 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 and resilient due to rougher normal 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. Various strategies for environmental management are being tested, in an attempt to achieve a sustainable balance between conservation and commercial exploitation.

Active avoidance of benthos contact requires appropriate motivation, and successful avoidance requires appropriate competence. Low impact diving training has been shown to be effective in reducing diver contact in suitably motivated divers. Experience appears to be the most important factor in explaining divers' underwater behaviour, followed by their attitude towards diving and the environment, and personality type.

All underwater environments frequented by recreational divers are potentially affected, but the impact is observed to be greater where there are large numbers of dives or the environment has fragile slow-growing organisms or delicate structures. The more obvious examples are tropical coral reefs and flooded caves with fragile speleothems. Relatively large numbers of studies have been done on tropical coral reefs as the pressure on them has been perceived to be highest. Coral reefs are to some extent self-repairing, and also sustain damage from non-anthropogenic causes, so an acceptable level of continuous diver induced degradation is theoretically possible, which would be matched by the natural recovery rate. Underwater speleothems, once broken, do not regenerate at all while the cave remains flooded, and remain broken forever, if human timespans are considered. Underwater cultural heritage in the form of historically important wrecks and archaeological sites are also susceptible to irreversible damage, but they are usually constantly deteriorating in any case. Diver impact mainly accelerates the inevitable.

Subtropical, temperate, and polar marine reef environments vary considerably in their ability to recover from damage, and have historically been considered less impacted by diving, consequently fewer studies are available on diver damage, reef recovery and sustainable carrying capacity. These areas are emerging as diving destinations, as is research on diver impact on their environments.

Research on the effects of divers on tropical coral reefs has shown reduced coral cover on heavily dived sites and a change in coral structure, with more resilient corals becoming dominant and a loss of species diversity over time. These reefs may be less resilient to other stressors like disease outbreaks and severe weather damage.

There is persuasive evidence that reefs can be damaged and the amenity value of dive sites compromised by badly planned or over-intensive tourist use. Marine tourism affects reef communities directly through disturbance such as structural damage to corals, boats grounding on reefs and damage by anchors, and indirectly through alteration of water quality by nutrient enrichment and pollution by toxic substances, waste water and increased turbidity. The level of degradation depends on the intensity, frequency, time and type of use and the specific environment.