Brightness Reef (1995) is, depending on how you look at it, either the fourth book of the David Brin's Uplift Series or the first book of the second uplift trilogy, which is a three book saga of the planet Jijo.
Jijo has been assigned by the Galactic Council as a fallow planet, where new, pre-sentient species must be allowed to evolve on their own without any Galatic species interfereing. The former leaseholders, the Buyur, left a million years ago, but remnants of that civilization still remain despite the Buyur's attempts at urban removal.
But that doesn't mean there are no galactic citizen species on Jijo. There are six: traeki, g'Kek, qheuen, urs, hoon, and, of course, humans. None should be here - they are all sooners who, if discovered by the galactics, would not only be criminals themselves, but their entire species would have to be punished for the crime. All six came for their own reasons, but mainly to hide in some way from galactive civilization.
To minimize their crime, the six have a religious fervor about their presence not affecting the planet. All that's built, from the smallest tool to the greatest building, must degrade within a few generations. And the degradation also includes the species' sapience itself. The zealots feel there is a Path of Redemption which all the six must follow, where eventually their sapience will disappear, leaving them prime fodder for some Galatic to come in, be their new patron, and re-uplift them, washing away the sins of the previously uplifted species.
Some feel this fervor more than others.
Events in this novel are set in motion when a spaceship arrives on Jijo. Are these the Galactics, who will hold judgment for the crimes of the six? Is it another group of sooners? Or something else entirely?
I found this novel harder to get into than the first three in the Uplist Series. Five new alien species, each with their own characteristics were quite confusing at first, especially since some chapters are written from the point of view of a member of that species. Also, I was expecting it to be a self-contained story, like the first three, but it is not. The saga continues for two more books.
That said, Brin once again has very good ideas. The ideas aren't as densely packed as the first three books (this book could easily be a hundred pages shorter), but it's still an enjoyable read for those who have already read the first three books of the Uplift Series.