Put the summary of the bug you're having here
What I expected to happen was...:
being able to swim in the water without any issues expecting none of my durability to go down on my elytra.
What actually happened was...:
when i landed in the water it continued my elytra flight even tho i was in the water and the durability went down.
Steps to Reproduce:
1. jump of a tall building or fly up with rockets
2. dive straight down into the water or glide smoothly down
3. and after u have landed check the durability of the elytra then after u have noted the durability begin to swim fast or slow and 30 seconds or so check the durability again and u will notice that the durability will have gone down.
Related issues
Comments

Thank you for your report!
We're actually already tracking this issue in MC-97190, so I resolved and linked this ticket as a duplicate.
However, that ticket has already been resolved. That means that this is not considered a bug and won't be fixed. Please do not leave a comment on the linked ticket.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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Elytra are still in use when you land in water swim, at least until you touch ground. Probably intended.