Even without underwater viewing (which is found elsewhere in the park for hippos) this huge pool is quite simply magnificent. Most zoos around the world have hippo enclosures that pale in comparison to this beauty! Also, if I'm not mistaken aren't there something like 15-20 hippos at DAK?
I suspect that since they made such an effort to showcase large groups of hippos in large habitats that they wanted to ensure optimal viewing of them while in the water. It must be a massive filtration plant nearby!