Never saw fletch, but I'm a fan of pretty much anything Chevy Chase so I'm sure it's good. And I'd believe that bill murray would have ad libbed the whole thing, that's his style, dude is hilarious!
It was where the water tower emptied on him at the train station. I think that was The General. Keaton also had a movie where a house wall fell down and he was standing where the window was. He did that stunt too. Brave people back then, hey?