See Water

In Real Life, it's very difficult to see underwater without wearing a facemask or goggles. Even things that are less than a foot away from your face come across as vague, indistinct blurs. This is because air and water have different refractive indices, and our eyes have adapted to focusing the light from the outside air through the (mostly watery) humors inside the eye onto the retina. When we replace air with water, the eye cannot physically adapt to different refraction angles and starts focusing the light far behind the retina, making all images blurry, at best. Read more about it here.

On top of that, depending on what's in the water around your head, opening your eyes can be anything from irritating to excruciating.

This is not the case in TV Land, however, where characters have the same crystal-clear visibility underwater as a camera lens, and can routinely read individual letters from long distances with their bare eyes.

A subtrope of Water Is Air.

Comic Books

 * Wavedancer elves in Elf Quest can see (and breathe) fine in air or water, as can Winnowill when she shapeshifts to aquatic form.
 * British comic character Fishboy (appearing in the weekly anthology Buster) was an amphibious Wild Child who also didn't need goggles underwater.
 * Justified in Marineman. The title character can see underwater without goggles, and when asked about it he explains that he has a transparent second eyelid.

Film

 * In  ~Atlantis: The Lost Empire~ , Milo Thatch reads ancient Atlantean underwater inscriptions with glasses on.
 * The glasses-on thing is the issue; While Milo could potentially see normally without glasses, having them on should just make everything a blur.
 * Inversion with Abe Sapien in the Hellboy films: He requires goggles (or in the second film, contact lenses) to put water around his eyes to see clearly through air.
 * Galen in Dragonslayer is able to determine
 * At the end of Mindhunters, the heroine and killer wind up in an underwater gunfight, in which they can clearly see one another's actions from a few yards apart. The heroine even mouths insults at her opponent, who gives her dirty looks in response.
 * Will in Pirates of the Caribbean: Dead Man's Chest has no problem opening his eye underwater and seeing the attacking Kraken.

Literature

 * The classic adventure novel The Coral Island by R.M. Ballantyne describes the characters swimming underwater and looking around at the marine life, which they can see clearly.
 * In Warrior Cats,  is able to see clearly underwater as he drowns.

Live Action TV

 * On Lost, nobody ever has problems seeing things underwater, from in Season 1, to  in Season 3, to  in Season 5.

Video Games

 * If a game features water, it's more likely to use this trope than not, so aversions:
 * Half-Life 2 has water that you can only see a few feet out from you in while swimming.
 * Despite this, that is only a fog that represents mud, pollution and other particles in the water. The underwater view is otherwise completely clear. However, Episode Two subverts this trope by adding a blur effect while underwater.
 * In Metroid Prime, your view is obscured underwater even though Samus already has a face mask. The powerup that lets you move freely in water also upgrades your visor so you can see freely, as well.
 * In Morrowind, unless you swim at exactly the right height, you can't see far.
 * In Minecraft, in addition to the general blue overlay and particles floating around, water gets darker the deeper down you go, making it impossible to see more than a few blocks down.

Webcomics

 * This Mias and Elle comic finds salt water in the eyes to not be very romantic.

Real Life

 * Many semi-aquatic animals have a transparent second eyelid that corrects for refraction and allows them to see clearly underwater.
 * The four-eyed fish, which spends its life at the surface of ponds and streams, has eyeballs with double pupils: an upper one for seeing in air, and a lower one for seeing clearly in water.