The first update we are talking about is the aquatic update.
The basic change of the aquatic update was to improve the oceans and add more sea creatures and structures to improve the challenge and fun of water.
The structures and new creatures that they created are at the list below.
Though if you do ever plan to play Minecraft I wouldn't suggest diving too deep or you'll drown.

Picture by Unknown from Heute.at
Some of the structures they addded include...
Some of the animals they added include...