Kelp looks solid from a distance

I can absolutely confirm this on 1.4.

Affects 1.6.0.6 beta

Thank you for your report!
However, this issue has been closed as Working as Intended.

It is by design that the level of detail changes as the player moves away, but the range at which this happens is linked to the render distance setting. If you need help or have a suggestion you might like to follow a link below.

Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Feedback – 📖 Game Wiki

The resolution should be reviewed. The range at which it happens isn’t linked to render distance at all, it always happens at the same distance.
I assume it’s because fog is much denser underwater so the game incorrectly assume the kelp is far away based on the fog density, so it turns solid right in front of you.

Also the kelp looks normal as soon as you exit water, so it makes no sense why your render distance suddenly weren’t enough as soon as you go underwater.
It makes sense to take advantage of the denser fog to cull more geometry but the game should better check if the geometry is actually obscured by the fog.