The sea creature is a cetacean that likely mutated from a species of dolphin or whale following the Great War.
The creature possesses similar physical attributes to dolphins, with gray-white countershading, a prominent snout, and a blowhole above the eyes. Unlike its relatives, the sea creature has a short, stubby dorsal fin and a jaw lined with large triangular shark-like teeth. Nearly all specimens bear scars, suggesting competition among their own species, or that they are subject to predation. Many dead sea creatures are found being fed upon by mirelurks.
The sea creature is always found deceased along the many coasts and rivers of the Commonwealth. Others appear to have been hauled onto boats by wasteland fishermen. Most can be found with their abdomens exposed, however, intact carcasses can be shot to cause the stomach to explode in a bloody fashion.
The sea creature was designed by Gabrielle Adams and created in ZBrush. It is referred to as the "exploding whale" in her ArtStation portfolio.
The sea creature found on the boat west of Beantown Brewery is a reference to the film Jaws. On the boat, a skeleton with a blue jacket, blue bandana and a machete can be found with a dead sea creature nearby. The outfit clothing and machete are very similar to the ones worn and used by Quint in the film, while the positioning of the sea creature matches that of where Jaws emerges and kills Quint. Underneath the boat, one will also find a diving cage resting on the river bed.