Dolphins, like most marine mammals, cannot smell while underwater. This is because their nose and sense of smell is their blowhole. The blowhole is used for breathing while breaching the surface of a body of water after extended periods of time underwater, and it must remain closed the entire time the dolphin is submerged. Since it is closed, the dolphin cannot use its sense of smell underwater. When a dolphin is above water, there is some evidence that it may be able to smell at a very low level.