When a sound vibrator produces sound waves inside water and encounters an interface, such as the surface of the water, the wavelength of the sound waves will change. The specific behavior depends on the properties of the two mediums involved.
When sound waves pass from one medium to another, their speed and direction may change, which affects the wavelength. In general, if the sound waves encounter an interface where the second medium has a different wave speed than the first medium, the wavelength will change while the frequency remains constant. This phenomenon is governed by Snell's law, which describes the refraction of waves at an interface.
In the case of sound waves passing from a material medium (water) to air at the water-air interface, typically the speed of sound in air is lower than in water. As a result, when sound waves transition from water to air, their speed decreases, and the wavelength also decreases. This is because the frequency of the sound wave remains constant, but the velocity changes, and wavelength is inversely proportional to velocity.
Therefore, at the water-air interface, the wavelength of the sound waves produced by the vibrator would decrease as they transition from water to air.