Since Know Your Meme doesn't give the reference for why it's a lake, maybe not everybody is familiar with british lore:
The mythical Lady of the Lake:
Probably best known via Monthy Python:
Strange women lying in ponds distributing swords is no basis for a system of government. Supreme executive power derives from a mandate from the masses, not from some farcical aquatic ceremony.
In short: She teaches Lancelot arts and writing, infusing him with wisdom and courage, and overseeing his training to become an unsurpassed warrior.
https://en.wikipedia.org/wiki/Lady_of_the_Lake
https://tvtropes.org/pmwiki/pmwiki.php/Main/EnigmaticEmpower...
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