Blue is the easy choice for a phone background and the easiest one to get slightly wrong. Too pale and your app labels sink into it. Too saturated and everything sitting on top looks tinted.
Water is also one of the few subjects that suits a tall screen. It reads as deep without needing a horizon, and it carries a lot of colour while carrying very little contrast.
Here is how to build an underwater lock screen that still lets you read the time.
Why blue and teal sit quietly behind text
Your eye locks on to differences in brightness far more readily than differences in hue. Blue and teal are a long way apart as colours but close in brightness, so the boundary between them is soft and nothing about it demands attention. That is why an ocean gradient can be full of colour and still feel like a background.
It helps too that water is naturally graded. Light falls off with depth, so an underwater image usually runs lighter at the top and darker at the bottom without anyone designing it that way. That is the shape a phone screen wants.
What deep water costs on an OLED screen
Most iPhones since the iPhone X use OLED, where each pixel makes its own light and a black pixel makes none. That is why a dark ocean scene draws less power than a bright one at the same brightness setting. LCD models such as iPhone XR, iPhone 11 and the older SE run a backlight behind the whole panel, so the image makes no difference there.
Worth knowing: the saving comes from the black, not the blue. Blue subpixels are generally the least efficient on an OLED panel, so a screen filled edge to edge with bright saturated blue is not a cheap image. A dark scene with blue in it is the version that helps.
Keeping the clock and icons readable over water
Nothing on the lock screen sits on a shaded plate. The clock, the date and any widget text are drawn straight onto your image, so legibility comes down to your choice of picture. Keep the top third calm and reasonably dark, and put the interesting part lower.
The home screen is slightly better protected. App labels are drawn in a light colour with a soft shadow behind them, but that shadow is thin, and a pale, busy patch of water will still swallow a long app name.
Tinted icons over blue backgrounds
On iOS 18 and later you can give home screen icons a Dark or Tinted appearance, with the tint picked by hand or sampled from the wallpaper. Sampling sounds sensible and backfires on ocean images, because it hands you a blue tint to place on a blue background, and the icons lose their separation from what is behind them.
Two better options. Use the Dark appearance, which keeps each icon's own artwork and darkens it, so shapes stay distinguishable. Or take the tint from a warm accent in the image, such as coral, sand or the orange on a fish, which contrasts with the water rather than joining it.
Depth is three layers, not thirty
Depth in a picture comes from a small number of cues: things in front overlap things behind, closer objects are larger, and distant objects lose contrast and drift toward the colour of the water between you and them. None of that requires detail.
So the strongest underwater compositions on a phone have three layers. A dark, simple foreground near the bottom edge, such as a rock shelf or a silhouette of weed. A mid-ground subject, one or two fish or a ray. And a graded background that pales toward the surface. More layers do not add depth, they add texture, and texture is what competes with your text.
Blur the home screen copy and keep the lock screen sharp
When you add the wallpaper, tap Customise, open the Home Screen panel, and turn on Blur. You keep the colours of the ocean scene exactly and lose the fine detail that was fighting your app labels, while the sharp original still greets you every time you pick the phone up. It is the fastest fix for an image you like but cannot read across, and one tap to undo.
Light shafts, caustics and what breaks at small size
Two ocean effects hold up at full size and cause trouble on a phone. Caustics are the moving net of bright lines cast on sand when the surface refracts sunlight. Light shafts are the beams angling down from above. Both are made of thin, high-contrast lines.
Thin bright lines are what a small screen handles worst. They shimmer, they break up when the image is scaled to fit, and they land in the middle band where notifications stack. If you want either effect, keep it soft and low in the frame. A wide, gentle glow from above reads as sunlight; a sharp beam behind your clock reads as a stripe. This is worth checking in a preview rather than after saving, which is why Aquarium 3D: Live Wallpapers puts the scene in a phone frame first.
Quick answers
What size should the image be?
At least your screen's own pixel dimensions, since iOS scales anything smaller up. Recent iPhone screens run roughly 1170 to 1320 pixels across, so something around 1500 by 3000 covers current models with room to reposition.
Why does my ocean photo look cropped badly?
iOS crops to fill a tall screen, and most underwater photos were shot wide. Pinch and drag in the wallpaper editor to choose which part survives, and favour a crop with open water at the top. Images built in portrait avoid the problem.
Can I make the clock stand out over water?
Tap the time in the wallpaper editor to change its font, weight and colour. A heavier weight helps more than a colour change, because thicker strokes cover more of the busy background. The real fix is still a quieter area of image behind it.
Does dark mode change my wallpaper?
On recent iOS versions the home screen wallpaper is dimmed automatically when the phone switches to dark appearance, and some wallpapers offer separate light and dark variants. Behaviour differs by version, so check the Customise panel on your own phone.
Where to get it
If you want ocean scenes framed for a phone rather than cropped down to one, Aquarium 3D: Live Wallpapers has reef, jellyfish, koi and deep sea scenes built vertically, with the open water where your clock goes and the subject lower down.
Pick the darkest one you still find interesting, blur the home screen copy, and give it a week.