If your kids haven’t already bugged you about it, the Minecraft Aquatic update has been released on some platforms. However, its still in beta on the Java platform for Mac and Windows. Here’s how to run the Minecraft beta (including the Aquatic update) on Windows 7,8 and Mac:
In the Java Edition, we put out regular test versions known as Snapshots: just go to the Launch Options tab, enable Snapshots, and then select the latest snapshot by clicking the arrow next to the Play button on the main tab.
Anything with a 1.13 release number should get you the Aquatic update.
Once in, create a world with 111 as the seed under “more options.”
Then when spawned in the world, go find an ocean. One should be close to you. Get a turtle shell so you can breathe underwater. And put some dolphin, turtle and tropical fish eggs in your inventory. Then you can spawn any of these creatures that you want in the water. Actually, it’s fun to spawn them on land too.