Bayona, who is best known for 2007 horror The Orphanage, admitted that the true-life drama – which follows a family's experiences during the 2004 Boxing Day Tsunami – was immensely challenging to make.
"I had all the difficulties," Bayona said. "Before we started to write the script, I called Guillermo del Toro, I told him the story, he loved it but he said, 'I would pay for not shooting that, Bayona!'
"He was telling me stories about James Cameron shooting Titanic... but the truth is I was so impressed and into the story that I never was worried about that."
Bayona also discussed the casting of Naomi Watts and Ewan McGregor in the lead roles, and the decision to change the family's ethnicity – in real life they are Spanish, where the film portrays them as British.
Digital Spy also spoke to Watts and McGregor about their experiences of the harrowing story.
The Impossible is out today (December 21) in the US, and January 1, 2013 in the UK.
Watch a trailer below: