Rain Wild Chronicles #1: The Dragon Keeper book by Robin Hobb

Too much time has passed since the powerful dragon Tintaglia helped the people of the Trader cities stave off an invasion of their enemies. The Traders have forgotten their promises, weary of the labor and expense of tending earthbound dragons who were hatched weak and deformed by a river turned toxic. If neglected, the creatures will rampage--or die--so it is decreed that they must move farther upriver toward Kelsingra, the mythical homeland whose location is locked deep within the dragons' uncertain ancestral memories.