Hafgúfa

Hafgúfa (Ocean mist) is by far one of the biggest cryptids out there (a lot bigger than the Bloop). It is like a Icelandic version of the famous Kraken, but a lot bigger. It is said that the Hafgúfa only eats once every 12 months, it opens it mouth and waits, then a lot of marine animals swim into it's mouth thinking that it's a cave/shelter, and at the right moment the Hafgúfa closes it's mouth. It sleeps 12 months and then wakes up, it is said to cause earthquakes and cause a super loud noise when it wakes up.

The loud noise
Long time ago, a group of seamen went out fishing. When they where in the middle of the sea they heard a loud noise and the ocean started to shake, they knew that it was the Hafgúfa waking up. So they sailed as fast as they could to their town and told the story.

1997/2003
Scientist heard a loud noise in the Atlantic ocean in 1997, it is said that it was a Hafgúfa waking up. It was heard again in 2003.