Jeremy Renner ''freaked out'' when he jumped into freezing water for 'The Bourne Legacy'.
The 41-year-old actor did his own stunts when working on the action movie and admits the icy swim was the toughest challenge of all.
He said: ''For all the stunts I was well prepared. But the water? Below 32 degrees? There was nothing I could do to prepare for that. And it freaked me out. Let's just say it wasn't very pleasant.''
The action star found fight scenes much easier to film, even though they caused some injuries.
He told Britain's Glamour magazine: ''Those scenes are like a well-oiled machine because they have to be smooth, fast and vicious.
''Of course, if you're doing hand-to-hand stuff, there are going to be black eyes. I had to give a few.''
The movie doesn't star the franchise's previous lead actor Matt Damon, but he was happy to give Jeremy advice on the film series - particularly when it came to the stunts.
Jeremy said: ''Damon's a good dude. I spoke to him briefly before I started on the film. He gave me one piece of advice and that was listen to the stunt co-ordinator, Dan Bradley, when it comes to the stunt stuff.''