Jacyuaruá, the Moon Mirror Lake, is part of the mythology of the Tupi-Guarani people of the Amazon, and it features in various legends. In one, female warriors dived into the deep lake and retrieved pieces of jade to carve into Muiraquitã amulets with supernatural powers that they gave to their lovers. While the women did the diving, the men drank fermented cassava juice and watched the football (probably).

“A frog, Iracema? It looks very much like an ordinary pebble. You didn’t carve it at all. You just found it on the shore, didn’t you? What about exploring the unknown depths, fighting the great river serpent for your betrothed?” … “No need to be rude.”

The story of Naiá gave the lake its name. Here is a condensed version from Portuguese Wikipedia:

 Long before the Portuguese came to Brazil, a young warrior called Naiá lived in a Tupi village. She had one desire, to be seduced and taken by Ja Cy, the moon mother, as the other young girls in her tribe had been, to shine as stars in the firmament next to Ja Cy.

 She searched through the mountains near her village every night, but Ja Cy never came. One night, deceived by the moon’s reflection on the surface of the water, she dived into a deep lake and drowned. Finally Ja Cy took pity on her and turned her into the Estrela das Águas flower.

The lake was the Moon Mirror Lake, and the flower, literally ‘Star of the Waters,’ was the Victoria amazonica, a lily which opens at night and can grow up to 40cm in diameter.

I suspect that this syrupy tale has more to do with the Portuguese settlers than with the myths of the Amazon tribes, in any case I used it as source material for the Inconstant Light story.