the photo makes it look larger than it actually is - when I was there I thought it was very small for the hippos - but yes, hippos in zoos almost always get stuck in very small enclosures. I think it might be because they spend most of the day in the water so people (presumably also the zoo designers) think that makes it okay. Put a rhino in the same size pen as hippos often get and there would be complaints about cruelty.
