The actor breaks down the splashy scene in episode 3 that gave him flashbacks to playing Aquaman on “Smallville.”

Warning: This article contains spoilers for Reacher season 3, episode 3, “Number 2 With a Bullet.”

In Reacher season 3, DEA agent Susan Duffy (Sonya Cassidy) says it best when she sees Alan Ritchson’s jacked titular hero emerging from the woods, naked and soaking wet, in the middle of the night: “F— me.”

The hardened agent has no idea what Reacher has just gone through to arrive that point in the season’s third episode, “Number 2 With a Bullet,” but viewers get the whole story in the scene prior — and it’s one of the most epic sequences yet on Prime Video’s action thriller.

While going undercover in a criminal organization to find and take down his nemesis Francis Xavier Quinn (Brian Tee), Reacher has no way to leave the heavily guarded house at night without being detected to meet up with the small DEA task force working with him. Since the main gate is being watched by a giant man unfazed by Reacher’s size (a feat no one thought was possible), the only way out is by sneaking through the backyard and swimming through dangerous waters to rendezvous with Duffy miles down the road.

Reacher makes his daring escape look downright easy as he climbs down massive rocks to get to the ocean, strips down to his tiny black undies, puts his clothes in a plastic bag, and dives into the water with his usual silent-but-chagrined grit. But filming that extended water sequence was a whole other story for series star Ritchson.

Alan Ritchson on ‘Reacher’.Prime Video

“It was tough,” the actor tells Entertainment Weekly with a laugh. “That water work was pretty tricky, and stripping down and crawling across those cold, wet rocks naked was not the funnest for me and for just about anybody watching — but we did it because we love the show.”

Reacher’s treacherous water escape is ripped straight from the pages of author Lee Child’s book Persuader, and Ritchson was dreading having to bring it to life. “Having read the book and enjoying it, that was the one [part] that I was like, ‘I hope we skip over that,'” the actor admits. “Maybe [Reacher] just crawls across the lawn, maybe he stays on the grass. But no, we actually built most of that world in a gigantic indoor pool. We had a wave-maker.”

Ritchson still can’t get over how massive the production design was for this scene. “I had some guys visit that have been on $400 million sets, like Aquaman, and sets that are just huge water world sets, and they’re like, ‘I’ve never seen anything like this for a water stunt,'” he says. “So yeah, it was crazy.”

In a strange way, it was also nostalgic for him. Ritchson’s first major TV role (other than his failed American Idol run) was playing Aquaman on Smallville from 2005 to 2010, and he jokes that the “flashbacks” to his time on that show were “jarring” as he filmed this episode of Reacher.

“Yeah, it was pretty similar,” he adds. “Because the water was cold, and when I was a child on Smallville, we were in a glacial lake. It was just above freezing, and it felt a little bit like that up in Toronto shooting again. So I was having flashbacks — it’s like my ‘Nam.”

Reacher season 3 debuts new episodes Thursdays on Prime Video.