Steps:

1. Create a flat world in Creative Peaceful difficulty.
2. Dig a 5x5 pool 1 block deep and fill it with water. Put some tropical fish in the pool (not necessary but fun to watch in the next step).
3. Put three axolotls in the pool.
4. Fly up until the axolotls don't notice you.
5. Wait.

Expected: Axolotls that leave the water return in time to save themselves from dying. Or, they don't venture away from water farther than some reasonable distance.

Actual: The axolotls leave the water and wander off. Sometimes they return, but eventually all the axolotls die from prolonged exposure out of water.

If an axolotl returns to the water, it eventually leaves again, stays out too long, and dies. I observed one meander back to the pool, but when it was two blocks away, it veered off and ambled away, and then flashed red and died - it could have made it back to the water easily.

This suggests either that axolotls aren't actually pathfinding to water, or their AI has no awareness of how long they've been out of the water and no urge to return.

Possibly related to MC-228464.

Update based on comment below: This apparently happens only when the water is 1 block deep. Axolotls don't venture too far from water that is deeper.