Going more than 128 blocks over an ocean laggs the game out

When going upwards over an ocean the entity count starts going crazy and the milliseconds per tick goes really high after you pass 128 blocks over the ocean level.

Suspect it's caused by water mobs spawning and despawning straight away because there are no players close enough

Short clip of this: https://youtu.be/BbdAD7nNMYQ