DolphinDolphins have to come to the surface when they rest in order to breathe, which they do consciously (ie by choice). If they didn't surface, they could drown
Bird
Waterfowl and wading birds, will sleep near or even on water. They tend to sleep in large flocks giving them protection and any movement on the water will alert them to predators nearby.
Giraffe
Giraffes need to sleep laying down but they do it very rarely. They would sit very low in the water, so swimming would take them much effort.
Walrus
Walruses can sleep in water! Sometimes, walruses will forage in places where there's no nearby ice or land for them to haul themselves out onto for nap.
Duck
The first grooming process is foraging, followed by bathing, after which the preening of their features becomes next and then lastly, sleeping.
Fish
Some fish float in place, some wedge themselves into a secure spot in the mud or coral, and some even locate a suitable nest.