Can someone help me remember this novel with a huge, blue sea monster on the cover?

I just remember that the cover had this giant leviathan (he/she looked angry) facing a teenager/young adult in a wooden boat in the middle of the ocean. The cover had an extremely weird effect on me, as I felt small and scared all of a sudden. But yeah, a big whale-ish monster thing looked like it popped right out of the water, ready to swallow the boy in the puny fishing boat. Also, the angle was pointed up at the monster, and you could see the back of the boy, if I remember correctly (it was near a decade ago and I was 6; sorry if this isn't completely accurate). Thanks!