Diver Rick Stanton praised the film's accuracy, saying the one cinematic change was that the cave water was muddy. The real divers had zero visibility, but "That would be impossible to demonstrate because then the viewers would not see anything."
Colin Farrell stated he experienced frequent panic attacks while underwater, and is hesitant to film any aquatic scenes in the future.
At the suggestion of Viggo Mortensen, Ron Howard added a scene during production of the boys left alone in the dark after the divers have discovered them.
Viggo Mortensen approached Ron Howard to suggest he and Colin Farrell do their own diving shots rather than using doubles; they'd been training with Rick Stanton and John Volanthen and didn't want to leave it to stunt doubles. Howard said it made his editing and storytelling easier.
Colin Farrell and John Volanthen frequently spoke over Skype. Farrell took up distance running, a hobby of Volanthen's. At the end of the shoot, Farrell completed the Brisbane Marathon. Around 33 minutes into the film, when the governor announces a stop to the rescue attempts until the rain stops, Farrell is wearing a Spartathlon T-shirt.