DragonVale: How to Breed a River Dragon
In DragonVale for the iPhone and iPad, the River Dragon is an uncommon hybrid dragon with both Water and Earth attributes that you can breed once you're level 14. It has a base breeding time of 13 hours, sells for 900,000 coins, and earns 17,500 XP for successful breeding.
To breed a River Dragon, you just need to breed an Earth Dragon and a Water Dragon, or hybrids that contain both of these traits plus one other trait. Iceberg + Sandstorm seems to a popular combination.