We may never know the truth about the Apkallu unless , of course, one day we encounter their descendants among the wilderness of stars. Coming closer to home, there are other monsters assumed to live in the waters of our own  world that crtainly do not come from outer space but  might as well do, so far are we from full knowledge of the mysteries of the ocean. Or even, it would seem, the mysteries of smaller bodies of water, namely lakes and rivers.