In the older version of Minecraft, the water would destroy any Minecraft or tracks he came in contact with. This has not been the case since the main update of Minecraft Caves & Cliffs Part 1. The tracks can be waterlogged and Minecarts can ride them under the sea, but there are four things that anyone who does an Minecart underwater cruise should know.
Minecarts are no longer destroyed by running water
If running water hits a Minecart trail of any kind, the trail will no longer be destroyed. Instead, it will behave as waterlogged until flowing water is sucked in, blocked or diverted.
Minecarts have a speed nerf underwater
Minecarts move at a much slower pace underwater. This means that you will not only move at a slower pace, but you will also have to use the motor rails at closer intervals.
Minecarts have no air source
You can still drown in Minecart. If you ride in an underwater mini-card, it is a good idea to wear a breathing helmet and / or a potion to breathe water.
Detector Rails are your friend
Detector Rails are the easiest way to power Powered Rails underwater, because water will destroy the Redstone and Redstone torches if they are touched by water.