Sea monster

Sea monsters are mythical or legendary creatures, believed to dwell in the sea and often imagined to be of immense size. Marine monsters can take many forms, including sea dragons, sea serpents, or multi-armed beasts. They can be slimy and scaly and are often pictured threatening ships or spouting jets of water. The definition of a "monster" is subjective, and some sea monsters may have been based on scientifically accepted creatures such as whales and types of giant and colossal squid.

https://en.wikipedia.org/wiki/Sea_monster