What is the name of the lake where the Doctor is killed in “The Impossible Astronaut”? The answer is Lake Silencio. The lake is the setting for the episode's shocking opening, in which the Doctor is apparently shot and killed in front of his friends.
“The Impossible Astronaut” begins with Amy Pond, Rory Williams, River Song and a younger version of the Doctor receiving invitations to a lakeside location in Utah. They watch as a mysterious astronaut approaches the Doctor. The astronaut shoots him twice, and he falls into Lake Silencio before regenerating, apparently exhausting his ability to survive.
The event becomes a fixed point that the travellers cannot simply prevent. They later discover that the astronaut is connected to River Song, while the Silence—a species that can be forgotten as soon as it is no longer seen—forms the larger mystery of the story. The lake scene is therefore both a murder mystery and a carefully arranged piece of the Doctor's future.
Lake Silencio is fictional, despite the episode's use of a real Utah setting. It should not be confused with Lake Windermere, Loch Ness or Lake Geneva. The lake's name is also a clue: “silencio” means “silence” in Spanish, echoing the season's recurring question, “Silence will fall.”