Goggles are one of the few pieces of equipment which can legally be used in competitions.
They have two compartments which fit over the eyes and an elastic strap which keeps them fixed to the head.
They serve two major purposes - protecting the swimmer's eyes from chemicals, harmful rays and damaging lights, and allowing the swimmer to see more easily underwater.
Goggles are particularly helpful to people who wear contact lenses, as they prevent them from falling out and getting lost.
You can even buy prescription goggles to help your eyesight underwater.
Most swimming pools contain a cleaning substance called chlorine.
This can irritate the eyes and cause temporary blindness, which is why long distance swimmers would struggle to get by without goggles.
They are relatively cheap and extremely useful for those long training sessions.