I'm sorry. This actually sounds so much like a Norse myth that I am a little confused by the wording. So "The Lake" is narrated by an old one eyed man, and it's about a hero that casts his eyes into a lake to become all-seeing and fight some kind of beast?

If so, this sounds almost exactly like the story of how Odin lost his eye. Odin left his possessions behind and went down into Midgard and then on to Jotunheim to find Mimir's Well. He disguised himself as a man to men and as a giant to giants and went by the name Vegtam the Wanderer.

Upon reaching Jotunheim, he ran into Vafthrudnir, the wisest of the giants. Vafthrudnir introduced himself as such and Odin knew it to be true.

Odin wanted to ask Vafthrudnir about the well, but first Vafthrudnir wanted to play a game of questions for the answer. Through his line of questioning, Vafthrudnir realizes he is speaking to Odin. Odin asks him what the price is for drinking from Mimir's Well. Vafthrudnir replies that Odin must sacrifice his right eye.

Hesitant to go plucking out his eye, Odin looks to Muspelheim and Niflheim, the lands of fire and ice. He realizes that without the wisdom from the well he will not be able to triumph over these primordial forces that want to return the world to darkness. Losing his eye was a terrible price, but he knew what he must do.

So he went to Mimir's Well in the roots of Yggdrasil. Mimir made sure Odin knew the price to drink, and Odin agreed. He took a horn full of water from the well and drank deeply. Upon drinking the future was opened up to him. He understood what would happen at Ragnarok (literally "the fate of the gods"); and how gods, men, monsters, and giants would all meet their fates. He also understood how to keep the world from falling into total darkness and destruction.

With his new knowledge, Odin plucked his own right eye out and tossed it into the well where it still sits shining out to anyone that passes by.

It sounds like your song has put Odin as the narrator rather than the hero of the story. He only loses one eye instead of both to become all seeing. And instead of a two headed beast, it's more like all the giants and monsters. It's also a well in the myth not really a lake.

The interesting thing about the Norse pantheon to me is that they have always been highly aware of their own mortality and exactly how it was going to end. It seems to shape how they interact with one another and with humans.