Longa, mas poderia ser ...
DragonSpell (DragonKeeper Chronicles, # 1) , por Donita K. Paul?
Da descrição da Amazon:
When Kale, a slave girl, finds a dragon egg, she is given the unexpected opportunity to become a servant to Paladin. But on her way to The Hall, where she was to be trained, Kale runs into danger. Rescued by a small band of Paladin’s servants, Kale is turned from her destination.
Feeling afraid and unprepared, Kale embarks on a perilous quest to find the meech dragon egg stolen by the foul Wizard Risto. But their journey is threatened when a key member of the party is captured, leaving the remaining companions to find the Wizard Fenworth, attempt an impossible rescue, and recover the egg--whose true value they have not begun to suspect.
Surgiu em uma pesquisa no Google por "dragon egg in a river" e parece corresponder.