The bug:

When the player is underwater, the game ignores the render distance setting and renders at the lowest possible preset (8 chunks). This results in excessive pop-in and low detail even at the highest render distance settings.

How to reproduce:

1. Set your render distance to 8 chunks.
2. Take note of how far blocks are rendered above water.
3. Go underwater (ocean biomes with kelp and seagrass are best to test this) and take note of how far blocks are rendered underwater.
4. Now, set render distance to highest setting available on your hardware. (For me, this is 72 chunks.)
5. Repeat steps 1 and 2, and notice how underwater render distance at higher settings doesn't differ from the lowest setting.

This is with 8 chunks render distance:

And this is with 72 chunks render distance: