Black Panther: Wakanda Forever is a film that centres primarily around the conflict between techno-futurist Africa and water Aztecs. A decision that resulted in like half the cast needing to learn how to swim, which inexplicably just so happened to include the guy cast to play a character who dropkick a blue whale into low orbit.
First though, the cliff notes version of the Wakanda Forever plot, the Black Panther dies leaving the usually formidable African nation unexpectedly weakened just as a formally hidden nation of fish people announce their intention to kick the living fuck out of anyone who tries to steal their precious vibranium. A fictional super-metal previously only thought to exist in Wakanda. Until now.
Anyway, a key change made from the comics concerning the aforementioned fish men is that they now hail from a Mesoamerican inspired land called Talokan rather than Atlantis. However, the idea of the country being wholly underwater was maintained, which necessitated the casting of actors and actresses who could swim like, really well because they wanted to film as much of the film as possible on location. Read: Underwater.
For example when deciding who to cast as the Submariner himself, Namor Marvel explictly asked actor Tenoch Huerta Mejía if he could swim before giving him the role. A question Tenoch answered by coyly telling producers …
"Well, I haven't drowned."
It would only emerge several months later when shooting formally began that Tenoch couldn’t actually swim and when asked why he said what he said earlier cheekily responded that he didn’t technically lie. Which is correct and if we’re being honest, something Namor in the comics would probably do.
In the end Marvel quite literally had to teach the actor how to swim, with him later recalling that they put him in floaties and threw him into a pool with actual children also learning how to swim. As a reminder, in the comics this character can swim at like 400mph.
The same is true of much of the returning Black Panther cast, the majority of whom could swim but not to a level where they’d look good doing so. resulting in Marvel also having to pay to teach them how to swim. Then you have Mabel Cadena who basically embarrassed the entire cast with her prodigious water-based athleticism.
Cast to play Namor’s cousin unimaginatively name Namora, Cadena was already a fairly strong swimmer (probably the strongest of anyone in the film) when cast but after training with a record-holding free-diver Cadena was able to hold her breath for in excess of 6 fucking minutes in full makeup and prosthetic that themselves took over 5 hours to apply.
According to Cadena herself she was actually disappointed in this as she would later learn that Kate Winslet had learned to hold her breath for longer than she could when making Avatar: The Way of Water.
However, it’s worth noting that according to Cadena’s trainer, she was one of the most naturally gifted free divers he’d ever encountered and he explained that if he’d just had one more week with her she could have easily learned to hold her breath for over 10 minutes if she really wanted to. An amazing fact that’s doubly hilarious when you realise that the person she was starring alongside playing the best swimmer in Marvel canon had to wear floaties for the first few weeks of production.