Doctor Who: 14 Cool Details Revealed In Steven Moffat's Wedding Of River Song Commentary
7. The Background Footage For The Doctor's Death Scene Was Captured During A Different Shoot
The Wedding Of River Song is an episode where the execution doesn't quite match the ambition of the script, with several moments feeling like they lack that extra bit of love and polish - just like this one.
The scene were we finally circle back to the start of the series and get to see the Lake Silencio confrontation from the Doctor's point of view should have been the standout moment of the episode, but instead, it falls a little flat because of how fake the whole thing looks - especially when juxtaposed with those insert shots from The Impossible Astronaut, y'know, the ones that were actually filmed in Utah.
Alex Kingston and Matt Smith are clearly stood against a green screen here, and it's so obvious that it proves to be a huge distraction while watching. It makes you wonder why the Impossible Astronaut team didn't shoot this scene while they were in Utah for real, but on the plus side, the production crew for that episode did have the foresight to grab some background footage of the lake, which was then used in the finale.
This is explained during the commentary, where Webb mentions that the Utah team shot a background plate for him to use during the Lake Silencio scene.
So, the footage behind Kingston and Smith (as seen in the above screenshots) was actually filmed on location, but it was then combined with the actors' performances via a green screen somewhere in Cardiff. Which is why it looks off.