Sepron The Sea Serpent (Beast Quest, Book 2)

One boy's journey to help his village becomes a quest to save the kingdom. Features a fearsome new beast in every book!
Floods. Starvation. Fear. This is what awaits the people of Avantia's coast if Tom and Elenna cannot stop Sepron the Sea Serpent. The huge and terrifying beast lurks in eerie waters. All the fish have fled and no boats dare to pass.
Tom and Elenna meet a mysterious stranger who may hold the key for tracking down the monster. But as they set off in a rickety rowboat, Tom can't help but wonder if they'll succeed so easily this time. . . .