So I have been working a lot in singleplayer 1.13.2 with my friend and we always have an elytra on our back.

As I was building a harbour with an aquarium, I often had the issue that my elytra activated in the water.

I dont really know how that happens, but it happens quite often.

This is annoying, because: 

You dont swim properly

You cant use underwater ladders to climb

It breaks the elytra

Id suggest, that the Elytra gets disabled, when underwater or in the water.