It takes place on a world totally covered in water. All their tools and supplies come from biological resources. Most material is made from plants and plant-like animals (like sponges). The hardest substance they have is bone. There is no metal (until they start bleeding themselves to get to the iron in their blood - ew) and communication is done by big semaphore towers.

This is true science fiction - a whole lot of science and not a terrible amount of story. Its saving grace is that its short and tight, and the science isn't flooding, just distracting. And there is story here to latch onto - the conflict of religion and science. A man dares to question why things must be as they are, and the priests don't much care for that. I like those kinds of stories (although there is some irrelevant stuff in the beginning that makes me question its relevance therein, and the romance is nil).