Question: How can you improve visibility underwater during swimming?
About the article "Human swimming", section "Accessories".

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The Race club utilizes specialized underwater photography equipment to create swimming technique videos, and can video a swimmer from under water or above the water to analyze swimming strokes underwater and from different angles to improve skill.
In addition, The Race Club sells swimming DVDs focused on swimming faster. 
 Ear plugs can prevent water from getting in the ears.
 Noseclips can prevent water from getting in the nose.
However, this is generally only used for synchronised swimming.
Using noseclips in competitive swimming can cause a disadvantage to most swimmers.
It is for this reason that noseclips are only used for synchronised swimming and recreational swimming.
 Goggles protect the eyes from chlorinated water, and can improve underwater visibility.
Tinted goggles protect the eyes from sunlight that reflects from the bottom of the pool.
 Swim caps keep the body streamlined and protect the hair from chlorinated water.
 Kickboards are used to keep the upper body afloat while exercising the lower body.
Pull buoys are used to keep the lower body afloat while exercising the upper body.
 Swimfins are used to elongate the kick and improve technique and speed.
Fins also build upper calf muscles.
 Safety fencing and equipment is mandatory at public pools and a zoning requirement at most residential pools in the United States.
Where intrusive underwater excavation is appropriate, silts and sediments can be removed from an area of investigation using a water dredge or airlift.
When used correctly, these devices have an additional benefit in tending to improve the visibility in the immediate vicinity of the investigation.
It is also important to note that for very deep sea excavation submarines are sometimes used to view sites.
Underwater photography can also be conducted from these submarines which assists the recording process. 
Silfra, by virtue of its location in the Þingvallavatn Lake, contains clear, cold water that attracts scuba divers drawn to its high visibility and geological importance; divers are literally swimming between continents.
The rift claims a shallow depth nearest to the bank, but deepens and widens further out.
Scuba diving professionals have divided Silfra into three sections: Silfra hall, Silfra cathedral and Silfra lagoon.
At its deepest, Silfra is 63 meters deep but diving this depth is seldom done and only by professionals.
In any case the most wondrous sights are in Silfra cathedral which is a 100 meter long fissure where you can see from end to end.
The rift offers amazing visibility and has been placed on the world's top 50 diving destinations.
The visibility reaches end-of-sight and is rated at 150 to 300 meters.
The general consensus of opinions from divers at Silfra is a feeling of flying, weightlessness and a number of divers have even described it as “as close to a space walk as one can get without being in space”.
Silfra is a dive site where even the best underwater pictures cannot give true justice to the real experience of being suspended in its clear waters. 
For scuba divers, the absence of a flow means that less effort is required to swim, and there is less likelihood of drifting away from a vessel or shore.
Slack water can reduce underwater visibility, as there is no flow to remove debris such as sand or mud.
In areas with potentially dangerous tides and currents, it is standard practice for divers to plan a dive at slack times.
For any vessel, a favourable flow will improve the vessel's speed over the bottom for a given speed in the water.
Difficult channels are also more safely navigated during slack water, as any flow may set a vessel out of a channel and into danger.