Axolotl movement

when I made a tank for my axolotl, all it did was stay to the ground, it wouldn't swim up no matter how big I made it. so I tried to make a 1 block high pond, and all the axolotl did was just sit there and do nothing, I put it on land next to the pond, all the axolotl did was walk to the pond and sit where it entered the pond and didn't move. please fix.