Esta parece ser uma referência a Drácula por Bram Stocker:
It is said, too, that he can only pass running water at the slack or the flood of tide.
-Professor Van Helsing no diário de Mina Harker, capítulo XVIII de Drácula por Bram Stoker
The Count, even if he takes the form of a bat, cannot cross the running water of his own volition, and so he cannot leave the ship.
-Professor Van Helsing no Jornal de Jonathan Harker, Capítulo XXV de Dracula por Bram Stoker