Sort of like the blob, this marauding slime with a voracious appetite was the top predator in its underwater environment (aside from a rare creature, nearly entirely made up of teeth) until a titanic underwater eruption sends it hurtling to the surface.
It makes its way into some marshes, where it feasts on snakes and frogs, until it makes its way into a local American town and is hunted back into the marshes and eventually (with fire) hounded back into the sea.
I remember that the creature was extremely sensitive to light, and could feel the light of the searching locals' torches through the black water of the swamps.
I believe this was one of a collection of short horror/sci-fi stories, and is quite an old story.
Is this ringing any bells with anyone?