Telaria

A Plesiosaurus called Plieo, who got somehow stuck in a big lake after following a school of fish during the ice age and had to devolpe and evolve to survive. At first she would attack and feed on the primitive men who were foolish enough to enter her lake somehow. But that only lasted so long as the rumors of this lake bein dangerous spread amongst the humans. Which in the end forced her to feed on the small fish at first and then the seaweed of the lake. After a while of eating seaweed instead of flesh, Plieo become more calm and less hostile towards living beings. Even so much that she would befriend certain forest animals around her lake, and even children who werent frighten of her since they didnt knew better yet. Though she still has this anger and fury towards adult humans, especilly men since they on occasion have tried to hunt her down and kill her, even though she hasnt done anything to them per say as she tends to sleep and be docile for years sometime. But as most humans would agrue with, she is a "monster" and needs to be dealt with before she dose any evil.

​The lake she is living and dwelling in, was made from a comet of stone and alien crystals, that crashed into the earth and creating a massive hole around it. Once the hole was filled by rain water and then later sea water by humans digging a canal to it, the comet was slowly buried into the bottom of the lake, and due to its special alien attributes it gave all the plant life in the lake a very sought out attribute; the gift of eternal yought and life. Which is what Plieo has used, without her full knowledge of it, for centuires to stay young. Which in turn explains how she has been able to live this long and even able to evolve during her lifetime. And since she has evoled into a herbivor then she will remain living in that lake forever, unless something were to happen and change that. Which could either be men trying to kill her due for various reasons, or it could be men trying to capture her and bring her away from her lake so that they could get the'ire hands on the comet or just the sea weed.

​Plieo got stuck in this lake as said above after following a school of fish. But how exactly this happend is pretty simple to explain. She followed them for a while due to bein straved and desperate, and therefor didnt notice the narrowing of her watery envoirment. After what seamed like an hour of following these fishes she passed underneath a valve alike opening in the mountains and then finally caught them in the lake. During her long hunted meal there was an earthquake that caused the mountain valve over the river between he lake and the sea to collapse and get blocked. It was then that Plieo surfaced and realized that she was in a big lake, in the middle of a tall forest that in turn was surrounded by snowy mountains. Cause her to be stuck in the lake with litterly no way out from it. She was devastated by this at first as any marine creature would be but it didnt take long until she was first visited by a human in a boat and she discovered that she had indeed a food source nearby; a human village.

​(Plieo is currently living in the bronze age but she can be found in pretty much any age of history, though i perfer to not pick modern age or even past Renaissance. Mostly because that wouldnt be as intressting but also because that would make the story into another Nessie one pretty much.)