[@Greenie] The World of Ice and Fire book talks about Rhoynish Water Mages that managed to resist the dragons. We aren't given any more information than that, but given that the Rhoynar worshiped the River I kind of imagine them to be an aquatic analogy to the Red Priests. 

There's no such thing as too long a bio in Advanced Roleplay, your character sheet is gold, put 'er in the CS tab.