If a wave is traveling at a constant speed and the frequency decreases, the wavelength would increase. This relationship is described by the wave equation:
\[ v = f \lambda \]
where \( v \) is the speed of the wave, \( f \) is the frequency, and \( \lambda \) is the wavelength. If the speed \( v \) remains constant and the frequency \( f \) decreases, the wavelength \( \lambda \) must increase to maintain the equation's balance.
So, the correct answer is: It would increase.