When holding space while flying with elytra landing in water causes the player to be either

be stuck at the surface of the water (making lots of mini jumps, unlike normal swimming).

or be flying under water (if the player is looking downward).

The player moves with flying speed in both cases.

Approaching a block to get out of the water, the player jumps up still flying and slowly descends on the ground.
The player model looks like it is flying all the time.