This quest was marked obsolete by Blizzard and cannot be obtained or completed.
Talk to Nat Pagle at Nat's Landing in Dustwallow Marsh.
Oh, I'm sure you and Babs had a good laugh over the outlandish descriptions and sketches in the book, but have you stopped to consider there might be some truth to the legends?
If you listen closely enough, I bet you can still hear sailors talk about Tethyr, the sea creature the book says lives right here! Of course, if you wanted to know for sure, you could always ask old Nat Pagle.
He's got a small fishing camp on a little island in Tidefury Cove, which is southwest across Dustwallow Bay.