Water does not cover/fill the entire river

Issue :

Water does not cover/fill the entire river

 

How to reproduce :
1. Create a new world with the following game settings :
Seed: 1920910235
Enable caves & cliffs experiment
2. Create the world and teleport to -195 63 -405
3. You'll find a river that's not entirely filled with water

Observed result :
The river is not entirely filled

Expected result :
The river is entirely filled with water