Tolkien wrote about two lakes; in my mind they connected, as perhaps they already had in his.
An encounter on the shore of Mirrormere in the Second Age.
OFC/OFC referenced/implied.
Character death implied.
One of the dwarves had spotted the intruder from the Gates, but as she approached, her feelings ran the gamut from caution to outrage to pity. The stranger was sobbing so—it was impossible to hold her disrespect of the holy lake against her.
‘Why are you weeping by Kheled-zâram?’
‘There was another lake that shone like dark glass,’ replied the elf. ‘We saw our faces mirrored, hers and mine, and above the mountain peak flamed white, like these. She is not here—and even the lake is under the sea.’
The dwarf put a gentle hand on her shoulder.
This was written for Silmladylove's prompt "kheled" (glass) and posted to Tumblr on 4 February. The prompt word is the first element in the dwarvish name of Mirrormere. It is also related to the (elvish) first element of Helevorn, a lake in drowned Beleriand. There is a bit of resemblance between the descriptions of Helevorn and Mirrormere, as well as between their names. (But it seems the Khuzdul name of Lake Helevorn is known and it did not contain the word "kheled").
100 words in MS Word.