In a time where priests, feigning loyalty to their gods, rule, a child will be born in the middle of the great desert. The prophecy acts as a warning for the creator (who may be a god incarnated or something of the sort ). In the sea, his mortal enemy grows. Perhaps a fish-man of some sort .

To gain victory over this foe, the creator must find a 'branch of fate', perhaps a branch off a sole tree in the middle of a forest, that some sort of tribe/community worship, saying it gives visions of the future for those who open their minds with it.
Next, he must find the tears of life. Perhaps the 'river of life' has a cave running underneath it, and down there is a pool. The river slowly seeps into this cave and as it goes through the soil, picks up salt, which crystallises after it drips into the pool. He must find a way to fuse the branch and crystals together to make a staff. (the branches of fate will provide a vision of where to find the destroyer, and the tears of life imbue the branch with the means to destroy him) He must make this weapon quickly, because the destroyer is using death, killing sharks, to obtain energy and mass required to make an army of shark-men, which can breathe air, as well as have gills. The destroyers purpose is to destroy life above ground.