The Aulake's Tides

Every day, the Aulake empties completely, only to fill back up by the next morning. Here's why: (Supposedly)

The Aulake's Tides

At the very bottom of the Aulake, there exists a narrow entrance to a grand cave system. These caves existed before even the Aulake did, back when Aulin was just one big crater. The Kreelis, a now defunct empire from the Fairre plains, built their very first capitol on the floor of the crater. They wanted close proximity to the cave, as the natural resources from the cave were incredible.
Down in the cave, not only were there beautiful gemstones and ores, but there was also a species of naturally growing fruit that required no sun to grow, Cresclines. Cresclines were very filling, and they had a dynamic spice to them that made them a popular trading tool. Blinded by hunger, greed, and the lack of sunlight that the caves let in, Kreelis miners exhausted all of the cave's resources without setting up a sustainable way to farm them.
This wasn't enough for the Kreelis. They needed more from this cave, so they made a deal with the sorcerer Falamantis. In exchange for a great deal of wealth, Falamantis would manufacture an extension to the cave. Falamantis pulled on some dark sources for this magic, and was impaled by the head of Kreelis's military mid-spell, as the Kreelis disagreed with Falamantis's entanglement in the dark arts.
Falamantis went missing after the casting of the spell, but the spell was finished. Unfortunately, the cave was cursed, and agents of vile darkness started appearing from the depths of the cave. Kreelis nearly fell after the discovery of the new caverns, but by some miracle, the gods intervened. Umberlee used the great power of the ocean to flood the Aulin crater with water.
Every day now, she floods Aulin with water, thus creating the Aulake. Mysteriously, the lake never stays filled. The water empties completely every night, and for a brief stretch of time, about 45 minutes, the cave is freely open. Perhaps there is a limit to Umberlee's power, or some great force that keeps her from filling the cave completely.
Some people speculate that Falamantis sits at the bottom of the cave system, with a spear through his decaying chest. Barely living, but limitlessly powerful, he empties the cave of water every night in order to preserve his ancient creation.

Accuracy

Most of this myth exists as a children's tale/religious story, and it should be interpreted as such. While Aulin can be visited, and the lake certainly fills every night only to empty during the day, there is no reliable documentation for Kreelis' capital city ever existing there. Kreelis is so ancient that it is difficult to find/trust any documentation from that period.
Kreelis certainly did exist somewhere though. So did Falamantis, though his resurrection as a lich has not been proven in any meaningful way. That being said, Aulin's caves are very deep and sprawling -- nearly endless. People still mine there, despite the risk of water crushing and drowning them. Many people go missing in those caves, but the potential profit is very tempting for ambitious miners.
As for creatures, there have been some strange sightings on the lakebed of Aulin after it empties each day. Usually the townsfolk say that these fiendish fish come from the ocean, but the more superstitious citizens blame the cave.