Lake Silencio was located in Utah, situated on the Plain of Sighs. According to Dorium Maldovar, it was a still point in time which the Silence of the Kovarian Chapter hoped would ensure the Eleventh Doctor finally died. (TV: The Wedding of River Song)
River Song was abducted by the Silence and Kovarian, placed in an Apollo spacesuit and submerged in the lake to await the Eleventh Doctor. This horrified her as it meant the tale about when the Doctor was supposed to die was true. (TV: Closing Time)
On 22 April 2011, the Doctor brought his companions to the lake for a picnic. During the picnic, Amy Pond saw a Silent in the distance, but promptly forgot about it when she looked away. Later in the picnic, the earlier version of River Song in an Apollo spacesuit emerged from the lake and shot the Doctor three times, apparently killing him. Amy Pond, Rory Williams, and River placed his body into a nearby boat, set it aflame with gasoline provided by an elderly Canton Everett Delaware III and pushed it into the lake. (TV: The Impossible Astronaut)
In an alternate timeline, River Song refused to kill the Doctor. This caused time to collapse. All of history happened at once. The Doctor averted this timeline by persuading River that his death was necessary and revealing to her that she had shot not him, but the Teselecta, which had taken the Doctor's form. The Doctor was present at his "death", but was safe inside the Teselecta and "barely got singed" by the funeral pyre. (TV: The Wedding of River Song)
Behind the scenes
Scenes located in Lake Silencio were shot at Lake Powell, in Utah.