Here an old map of Duisburg, when they still had Belugas and the River dolphins
As you can see, the Belugas and dolphins were more or less placed "randomly" in the zoo. Next to tigers and the "Chinese garden" The River dolphins were in the old aquarium first, but years later Duisburg built the "Rio Negro hall", where the 2 were moved and displayed along to other Amazonian/South American animals (like the giant otter).
https://zoo-duisburg.de/lageplan (here is a link to the more or less actual plan, the River dolphin is still shown on the map, though. Without the belugas you could even say the bottlenose dolphins look now even more "random" on the map.
Nürnberg has their dolphins together with sea lions (to some degree, at least) and next to the manatee house. As far as I know they share the same underwater viewing area, meaning you can look at the dolphins from one side and then turn around to see the manatees. As you can see most of their neighbours do look kinda random, even though, yes there is an aquarium near by.
Now Loro Parque does have many fully aquatic animals, but they also didnt place them all in the same area. The dolphins and orcas are next to each other, however the tigers are also their neighbours.
My last example is from the Brookfield zoo.
The dolphins there are placed next to sea lions and/or seals and also close to the big cats. (there must be something about placing dolphins close to tigers

)