Whales And Dolphins Look A Lot Like Fish But They Are Really sea going mammals. Like all mammals they breathe oxygen From the air and so must surface to breathe . One or two nostrils called blowholes on top of the animals head allow it to breathe without lifing it's head from the water. But dolphins and some whales sometimes rear right out of the water to look around a technique called spy-hopping.
img source: https://www.express.co.uk/news/world/595103/Craig-Ison-Evans-Head-shark-attack-Great-White-Australian