This is the offshoot I mentioned of this question.
According to this,
In a few tales, a maiden or a fay had trapped Merlin in an enchantment. The most famous was the Lady of the Lake. Again, there are few versions involving his death at the hand of the Lady of the Lake.
The Lady of the Lake was a powerful sorceress and the lady of Otherworldly realm, hidden by the illusionary lake. The Lady of the Lake was known by several other names, such as Niniane, Viviane and Nimue. Further confusion resulted when some author listed several women with title the Lady of the Lake.
Following a link,
There seemed to be several "Lady of the Lake". The most important Lady of the Lake was Niniane (also known as Viviane, Vivien or Nimue). Some even say that Morgan le Fay was also the Lady of the Lake, though most often Morgan was referred to as one of nine sorceresses of Avalon.
The Post-Vulgate Cycle's second Lady of the Lake is called Ninianne, and her story is nearly identical to the one in the Lancelot-Grail, though it adds her bestowal of the magic sword Excalibur to Arthur. Sir Thomas Malory also uses both Ladies of the Lake in his Le Morte d'Arthur; he leaves the first one unnamed and calls the second one Nimue.
It seems like the "some author" mentioned in the first quote is Sir Thomas Malory.
Is there any connection between the two Ladies of the Lake, given that Malory implies that they are separate figures?