Game Freezing

Put the summary of the bug you're having here

What I expected to happen was...:
To not lag extremely?

What actually happened was...:
I made an "amplified" biomes world and in the world i normally get around 140 fps in game even when it's generating new amplified chunks but at random times it freezes up completely for about 15 seconds especially when swimming or falling into water.

Steps to Reproduce:
1. I am not completely sure how to reproduce it BUT
2. Create an amplified biomes world (i made it hardcore but i don't think that matters too much)
3. go swimming and falling into water from very high places
4. Still not sure how to reproduce it exactly though...