If you think birds might use the fountain, please add something in the tiers to allow birds to get out. If the water is too deep they can’t climb out and they drowned. Also, to help keep you water clear get a bundle of barley straw. They are sold at farm stores for stock tanks. A garden store charges way more for the same thing. These will reduce algae growth. Good luck.
If small animals get in there for example shelter during cold season they could be stuck not getting back up, so I recommend you to put something in the bowl as a ramp to climb back up. Even for the warm seasons of course with the possibility of animals drowning.