Dolphins are able to hold their breath for 15 to 17 minutes underwater. Dolphins are actually a type of whale, and they breathe through their blow holes.
With the inability to breathe underwater, dolphins are unihemispheric sleepers. This is the process of shutting down one half of the brain while the other half remains alert. This sleep pattern allows dolphins to alternate each side of a sleeping brain, ensuring that they obtain an equal and adequate amount of sleep. This provides dolphins with the ability to recharge while still being able to naturally swim, stay away from potential predators and breathe.