thalassophobia

You worked at a lighthouse offshore, you usually had your own boat to leave. After a week had passed, it was time for you to go home. You gathered your things, got into your boat, and started sailing. As you sailed, you began to hear strange noises coming from underwater. You didn't look down, but you saw nothing. Fear began to take over. You didn't know what to do, so you just sped up the boat. After hours, night had fallen. You decided to sleep while letting the boat drift. In the middle of the night, the sounds returned. This time... in the distance, you saw a huge figure diving into the water again. Terrified, you grabbed your harpoon, even knowing it would probably be useless... Now... hope that whatever is underwater isn't hungry...

The creature's name is "Tide Eater," and it's an irrational being that attacks on instinct. It attacks boats, ships, airplanes, warships, cargo ships, etc. When a ship is attacked by the Tide Eater, almost 98% of the people die. Those who survive say it's gigantic, capable of piercing through the clouds.