Abaia/ Large Eel

Classification: Mythological

The Abaia was, supposedly, a giant, magical Eel that lived in the bottom of several lakes. This magical eel killed any creature that harmed or disturbed the other inhabitants of the lake (the fish). This is because it saw the fish as it's children and any creature that dared to harm or disturb them was immediately overwhelmed with a large wave, cause by the Abaia's powerful tail, thrashing underwater. In the case of humans, this was usually fatal for humans because it sank the ship they would fish from.

In another form of this story, the Abaia causes a great rain to flood the lake and kill anyone who harms or disturbs it's children or itself. An example of this is in the following story:

One day, a man discovered a lake in which were many fish, at the bottom of the lake lived a magic eel, but the man knew it not.
He caught many fish and returned the next day with the people of his village whom he had told of his discovery, and they also were very successful, while one woman even laid hold of the great eel, Abaia, who dwelt in the depths of the lake, though he escaped her.
Abaia was now angry at the village people, for his fish had been caught and he, himself had been seized, so he caused a great rain to fall that night, and the waters of the lake also rose, and all the people were drowned except for an old woman who had not eaten the fish and saved herself in a tree.

As this story shows, the Abaia ferociously protect it's children and is willing to go to any measures to prevent any creatures from harming or disrupting them (or punishing the wicked that do).
Though there are stories in many mythologies about large Eels, Eels of that size are incredibly unlikely. The reason most of these creatures are classified as myths instead of cryptids is because of their supposed magical properties. Though they are interesting, Cryptozoology is the search for new species of animals, the fact that these creatures are usually magical makes them of little interest for cryptozoologists.