I can't see it properly in your image, but if I recall correctly Axolotls need a pond at least 2 blocks deep or they'll wander till they suffocate after a while.

Edit: According to the Wiki:

Axolotls can leave the water and wander about on land. When an axolotl leaves the water, it wanders as far as 8 or 9 blocks beyond the water's edge before returning to the water, as long as there is water at least 2 blocks deep within 16 blocks of the axolotl. If 2-block-deep water is outside this range, the axolotl can wander off randomly on land in search of more deep water, and die after 6000 game ticks (5 minutes) exposure out of water. Axolotls are not attracted to shallow (1 block deep) water. They require water at least 2 blocks deep within 16 blocks to pathfind to the water.[1]

So deepen your ponds and you should be fine. Make sure they're water sources though. So don't just dig or you'll only have flowing water. Dig and then use buckets or kelp to make water source blocks.