Most versions of the Arthurian legend relates that, after the Battle of Camlann, a dying King Arthur ordered a surviving knight - usually Sir Griflet or Sir Bedivere - to dispose of Excalibur in a nearby lake. The knight however hides the sword twice and lies to Arthur, who sees through the deception, before finally throwing Excalibur into the lake. Then a hand reaches out from the water and snatches it.
Then Sir Bedivere departed, and went to the sword, and lightly took it up, and went to the water side; and there he bound the girdle about the hilts, and then he threw the sword as far into the water as he might; and there came an arm and an hand above the water and met it, and caught it, and so shook it thrice and brandished, and then vanished away the hand with the sword in the water. So Sir Bedivere came again to the king, and told him what he saw.
It is commonly said that the sword was thus returned to the Lady of the Lake, but how is that known? It doesn't seem to be the same lake where Arthur received the sword from originally. Moreover, which lady would it be? Nyneve, Nymue, or some other unnamed entity?