Leviathan

Leviathan is an indestructible enemy in Tomb Raider: The Angel of Darkness, in The Cabal headquarters in Prague.

Biography
Grotesque, as well as powerful, the shark-sized Leviathan is a monster that prowls the waters of the Strahov Fortress. A gaping maw sits at the end of its sinewy body and tail, its yellow-and-black color scheme inflicting a sense of danger before the being attacks. If you are in the water when you see one, remove yourself as quickly as possible. One speeding thrust and it will lacerate you to death. Stay on dry land (where the creature cannot follow). Do not move near these creatures, and if you are caught near one, swim directly to the nearest ledge to climb out.

Reference
Левиафан