How do movies film underwater?

With Black Panther: Wakanda Forever and the upcoming Avatar: The Way of Water both shooting extensively underwater, it seems filming wet is the new dry. But how do filmmakers do it, and with modern special effects technology, why bother taking the plunge at all?

Anyone who’s ever tried to dry a phone out in a bowl of rice knows that submerging delicate technology in water rarely ends well. And yet, for almost as long as we’ve been making film cameras, we’ve been trying to point them at stuff underwater. It’s pretty much as difficult as it sounds, too. On top of the obvious technical problems, shooting in the wet is usually a logistical nightmare, and an expensive one at that.

So how do these crazy cats do it?

Well, the first problem with filming underwater is that, inevitably, cameras are just brimming with electric, which doesn’t tend to perform all that well in damp environments. They have to be sealed against high pressure, and remain operable even in low-light conditions while wearing a scuba mask.

The first filmmakers to get around this problem were the Williamson brothers, who pioneered the first commercial use of underwater film in a silent adaptation of Jules Verne’s 20,000 Leagues Under the Sea all the way back in 1916. Their innovation? A big metal tube with a house on the end, or, to use the technical term, a “photosphere.”

This tube hung off the side of a barge, then a camera operator would have to climb down into a 5-foot observation chamber and get filming. It sounds like a lot of effort, but the shots of tropical fish and divers walking on the sea floor are pretty mind-blowing for something made over 100 years ago.

The next proper go at aquatic cinema wouldn’t see the light of day until 1954 (be nice, there was a lot going on) when, coincidentally, Walt Disney Studios also adapted Verne’s masterpiece in their first live-action movie for the big screen. There’s a fantastic behind-the-scenes documentary on this film available on YouTube, but long story short, it wasn’t the easiest picture to shoot. By this point, camera technology had progressed enough that the crew could use pretty standard-looking apparatus (with a bunch of extra housing and waterproofing, of course). But, technical aspects aside, the crew still had to contend with moray eels, sharks, experimental diving equipment and, bizarrely, a lack of sunlight in their shooting location off the Bahamas.

It’s hard enough to film underwater when the cast are canonically wearing diving suits, but while acquiring gills through a genetic mutation is pretty convenient for a character in a movie, it turns the whole filming process into a bit of a nightmare. Even today, actors overwhelmingly favour lungs, and they tend to get a bit precious about being able to breathe, thank you very much.

There’s a reason Waterworld accidentally became the most expensive movie of all time on its release in 1995, and it wasn’t to persuade Kevin Costner to drink his own wee. With hurricane warnings, destroyed sets and Costner’s stunt double almost lost at sea, filming on water was dangerous enough, let alone under it. And that’s before the film’s stunt coordinator, Norman Howell, suffered compression sickness from the few underwater shots in the movie, and had to be shipped to a Honolulu hospital for a few days.

With Waterworld’s notoriously choppy production, it’s a miracle anyone’s suggested filming underwater since. But even when everything goes according to plan, shooting in the wet is hardly a walk in the park. The fourth instalment in the Potter franchise, Goblet of Fire, was considered nigh unfilmable before Mike Nichols took up the director’s mantle, not least because of the extended underwater sequence slap-bang in the middle of it.

Perhaps because a Scottish loch looks a lot less inviting than the Hawaiian coast, Potter producers elected not to submerge their young cast in a real lake, and built a nice indoor one for them to use instead. But massive purpose-built pools don’t come cheap, and at sixty square feet with a capacity of up to two million litres (the largest of its kind in Europe) this one was pricier than most.

And that’s before you even start shooting the thing. In a recent interview with GQ, Daniel Radcliffe revealed that during filming for the second task the crew produced an average of seven seconds of usable footage each day, constantly stopping to work out technical problems, or to administer that anathema to speedy film production, oxygen.

So why bother? It all seems a bit of a faff, right? And with modern CGI getting pretty nifty (it’s amazing what they can do with computers these days), who can blame a movie like James Wan’s Aquaman for abandoning the underwater camera housing for a blue screen and an octopus playing the drums?

Well, the results, it seems, speak for themselves. Despite coming out in 2005, something like Goblet of Fire holds up impressively well by blending underwater photography with CGI. And it’s no accident that Ryan Coogler’s latest Black Panther flick has seemingly broken Marvel’s run of dodgy special effects by filming its underwater sequences in a fish tank. 1954’s 20,000 Leagues and 1995’s Waterworld, meanwhile, still look incredible, even without much of the computing power of later flicks.

Which brings us right up to the modern day, and James Cameron’s long-awaited sequel, Avatar: The Way of Water.

From what we’ve seen so far, it looks like a lot of the film takes place down where it’s wetter (Zoe Saldana recently revealed she held her breath for almost five minutes at a time to get the aquatic scenes right). If nothing else, it seems Cameron is looking to flex his VFX muscles once again by tackling a water-based film, and the combination of CG with a real water tank is presumably a key part of that.

So what’s the takeaway? I suppose the big one is that filming underwater is bloody difficult. But maybe that’s part of the reason filmmakers keep coming back to it. It’s the ‘how the heck did they do that?’ effect, the same thrill we get watching Tom Cruise strap into a jet or throw himself off a cliff.

If it’s not to grandiose, we could paraphrase JFK here: we don’t do these things because they’re easy. We do them because they’re hard. And, sometimes, wet.

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