Question: What is the practice of swimming on or through a body of water while equipped with a diving mask, a shaped tube called a snorkel, and usually fins?
About the article "Snorkeling", section "Abstract".

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  Swimming, including pool swimming and open water swimming  Diving off springboards or off platforms  Modern pentathlon includes épée fencing, pistol shooting, swimming, a show jumping course on horseback, and cross country running  Rescue swimming is swimming with the goal to rescue other swimmers or the practice thereof.
Snorkeling is the practice of swimming at the surface (typically of the sea) being equipped with a mask, fins, and a short tube called a snorkel.
Synchronized diving  Synchronized swimming is a hybrid of swimming, gymnastics, and ballet.
Triathlon, a multi-sport event involving the completion of three continuous and sequential endurance events, usually a combination of swimming, cycling and running  Waboba is played with a waboba ball on beaches or in pools.
Water aerobics is aerobics in the water.
Water polo is a team sport played in water.  
Snorkeling (British and Commonwealth English spelling: snorkelling) is the practice of swimming on or through a body of water while equipped with a diving mask, a shaped tube called a snorkel, and usually fins.
In cooler waters, a wetsuit may also be worn.
Use of this equipment allows the snorkeler to observe underwater attractions for extended periods of time with relatively little effort.
Snorkeling is a popular recreational activity, particularly at tropical resort and scuba diving locations.
The primary appeal is the opportunity to observe underwater life in a natural setting without the complicated equipment and training required for scuba diving.
It appeals to all ages because of how little effort there is, and without the exhaled bubbles of scuba-diving equipment.
It is the basis of the two surface disciplines of the underwater sport of finswimming.
Snorkeling is also used by scuba divers when on the surface, in underwater sports such as underwater hockey and underwater rugby, and as part of water-based searches conducted by search and rescue teams.
A swimmer's snorkel is a tube typically about long and with an inside diameter of between , usually L- or J-shaped and fitted with a mouthpiece at the lower end, and constructed of rubber or plastic.
It is used for breathing air from above the water surface when the wearer's mouth and nose are submerged.
The snorkel usually has a piece of rubber that attaches the snorkel to the outside of the strap of the diving mask.
An older technique is pushing the snorkel between the mask-strap and the head, but this practice increases the chances the mask will leak.
The optimum design length of the snorkel tube is at most 40 centimeters (about 16 inches).
A longer tube would not allow breathing when snorkelling deeper, since it would place the lungs in deeper water where the surrounding water pressure is higher.
The lungs would then be unable to inflate when the snorkeler inhales, because the muscles that expand the lungs are not strong enough to operate against the higher pressure.
Snorkels also constitute respiratory dead space.
When the user takes in a fresh breath, some of the previously exhaled air which remains in the snorkel is recycled into the lungs, reducing breathing efficiency and causing a build up of carbon dioxide in the blood, which can result in hypercapnia.
The greater the volume of the tube, and the smaller the tidal volume of breathing, the more this problem is exacerbated.
A smaller diameter tube reduces the dead volume, but also increases resistance to airflow and so increases the work of breathing.
Occasional exhalation through the nose while snorkeling will reduce the build up of carbon dioxide, and help in keeping the mask clear of water. 
Methods of underwater diving.
Diving without breathing apparatus.
Underwater diving without breathing apparatus can be loosely categorized as underwater swimming, snorkeling and free diving.
These categories overlap considerably.
Several competitive underwater sports are practiced without breathing apparatus.
The ability to dive and swim underwater while holding one's breath can be a useful emergency skill, and is an important part of water sport and navy safety training.
More generally, entering water from a height is an enjoyable leisure activity, as is underwater swimming without breathing apparatus.
Free diving does not involve the use of external breathing devices, but relies on a diver's ability to hold his or her breath until resurfacing.
It includes a range of activities from simple breath-hold diving to competitive apnea dives.
Fins and a diving mask are often used in free diving to improve vision and provide more efficient propulsion.
The use of a short breathing tube known as a snorkel allows the diver to breathe with the face remaining immersed, while at the surface.
This may also be used when no diving is intended, and the snorkeler remains at he surface. 
[[File:AnnotatedOctopushPlayer.png|left|thumb|200px|Annotated Player 1. snorkel and mouthguard 2. hat with earguards 3. mask 4. fins 5. stick 6. puck 7. glovePlayers wear a diving mask, snorkel and fins, and carry in one hand a short stick for playing the puck.
A full list of equipment is given below: