When using a controller you toggle crouch instead of holding down the crouch button. However when you are underwater you are unable to toggle your crouch while you are standing on a solid block. Instead you have to hold down the crouch button which is awkward on a controller. I am not sure if the toggle crouch works underwater on tough controls.

Steps to reproduce:
1. Play minecraft with a controller
2. go underwater, stand on a solid block and attempt to toggle crouch