Confirmed in 1.13.1!
Confirmed in 1.13.1
Confirmed in 1.13!
When you looking from top on a huge source water field (20x20 and 2 high) and the ground is made of soul sand the fps drops to 1-2. From side it's not so drastic.
Confirmed in 1.13 and18w32a!
Confirmed in 1.13.2