Axolotls frequently get stuck inside of waterlogged blocks like coral or sea pickles. It seems like they have the same speed as on land when inside of such a block.
Linked issues
Attachments
Comments

Seems like they can't pathfind properly when inside of waterlogged blocks, like coral or sea pickles. They get stuck there for a while until they can free themselves. Seems like they have the same speed as on land when inside of such a block.
Relates to MC-208586.
Can confirm in 21w03a.
Can confirm in 21w11a.

I'm seeing this issue, or one very similar, in 1.17.1 full release. I've had 4 axolotl's stuck trying to swim through wall blocks for days now (realtime, weeks in minecraft). Every axolotl I put in this pond has the same issue, its just a matter of time.
[media][media]

I am still seeing this issue in both 1.19 and 1.20 versions of the game. I've attached a screenshot, it seems to be primarily sea pickles that they get stuck in.
Maybe relates to MC-206401