Why is my GoPro dive footage blue, and how do I fix it?
Because the water took the red out of the light before it reached your lens. It is not a fault in the camera, and a better camera does not change it.
What the water does
Water absorbs light, but not all colours alike. Red goes first. In clear water most of it is gone by somewhere between 5 and 10 metres, orange follows, then yellow, then green, and blue travels furthest. The numbers move with the water. Green coastal water with a lot of plankton behaves differently from the open blue sea.
The light also has to make two trips: down from the sun to your subject, and from the subject back to your lens. So distance counts as well as depth. A fish three metres away at 5 metres has lost more red than the same fish at arm’s length, which is why underwater photographers say get closer, then closer again.
What you can do in the camera
White balance first. Automatic white balance copes in the shallows, but at depth there is little red left to scale up, and it can wander during a clip. If your GoPro lets you set white balance by hand, fixing it at one Kelvin value instead of Auto gives steadier footage, though not more red.
A red filter in front of the lens removes some blue and green, so the little red that remains takes a bigger share. It works in a band, from a few metres to somewhere in the teens. Too shallow and everything turns red. Too deep and there is no red to lift. It also costs light, and in green water you need a magenta filter instead. A video light brings the colours back, but only within a metre or two, because its light crosses the same water.
What correction afterwards can and cannot do
Software does roughly what the filter does, but after the sensor: it multiplies up the red that was recorded. That only works on red that reached the sensor. At 5 metres there is still enough, and the correction is gentle and clean. At 15 metres there is a little, and lifting it lifts the noise with it, so the shadows go grainy and the compression shows. At 25 metres almost none arrives, and what comes out is a believable guess, not a recovery.
That is why a clip from 25 metres will never look like one from 5, however good the software is. It will look much better than the blue original, and that is the realistic aim. The best colour on a dive is shot in the first ten metres, close to the subject, with the sun behind you.
What I wrote for it
A dive is also forty minutes that nobody will watch, so I wrote Surface Interval to do both jobs. You add the videos from a dive, from Photos or from a card reader through Files. It measures each clip and puts back the colour the water took, shallow, mid, deep or night, read from the footage rather than from a preset you have to guess at. Footage that a camera has already corrected is recognised and left alone, so it is not corrected twice. Then it finds the moments worth keeping, trims them, keeps them in the order you shot them and puts music under them. You choose how long the reel is.
It works with GoPro, DJI, Insta360, an iPhone, anything that writes an ordinary video file. Nothing is uploaded; it all runs on the phone or the Mac. It is free for two reels a day, each with a small watermark, on iPhone and Mac. It cannot give you red that was never recorded, and I would rather say so here than let a 30 metre clip promise otherwise.