What is the climax of "By the Waters of Babylon"?

You have asked a very good question, and obviously many will differ in their thinking on this story. For me, however, the climax of this story is John's discovery of the "dead god" in the last few paragraphs of the tale. Following the amazing vision that John has of "the gods" and their lives before the "Great Burning", John describes himself as "confused" - he is not able to understand the reason for the destruction. John's discovery of the "god" and his resulting conclusion that he was a man like him represents the end of John's quest for knowledge and self-discovery, his journey to find his own identity and that of his people. It is clear however, that the way the "dead god" is described in his posture and the way that he would have watched his people die gives John vital truth about the nature - and dangers - of knowledge, and hopefully points our fictional descendants in a different path from the abuse of knowledge leading to the destruction of mankind.