Even in the first Avatar movie, Cameron's love of the ocean was apparent. The Christmas tree worm-type plants, and jellyfish-creatures floating in the jungle.
Cameron, a Canadian from Kapuskasing, Ontario learned how to scuba dive in a pool, but fell in love with the ocean upon moving to California and doing his first open-ocean dives. He has been quoted saying "I do an awful lot of scuba diving. I love to be on the ocean, under the ocean..."
I think it's a great way to raise awareness of the oceans, one what is presumably going to be another highest grossing box office hit.
As it is Saturday night, if you have not watched it, I highly recommend another movie he directed, The Abyss. A classic movie about the ocean and how extraordinary life on this planet really is; climaxing in one of the greatest Director's Cut endings ever.