This is a bug that lets you fly without the elytra and swim on land like a dolphin.

I found some reports stating this, they were not very accurate so here a detailed description.

Description:
In the video(Was too big for atachment so here you go https://www.youtube.com/watch?v=xJDrRXESTag&feature=youtu.be ) you can see how this bug is "done".
Basically: You have to fly very fast, glide down slowly and then take off your elytra.(At least that's what I am thinking) When landing in water/cobweb, etc. you can survive the fall and "swim" on land.

I hope this helped!