Read Psalms 104:24-26  These verses tell us that God is great and has made the huge seas.  It also tells us that God made the creatures in the seas, both great and small.  Verse 26 mentions leviathan as one of the creatures that play in the sea.  Leviathan is also mentioned in Job 41.  It is mentioned as a great and powerful sea creature.  This is probably the ancient dinosaur sea creature, the plesiosaurus. God made everything in the six days of creation.  He made the sea creatures on day 5 and the land creatures and man on day 6.  Wouldn't it be fun to swim on the back of a plesiosaurus?  I'll bet he could go fast!