Abstract: A wave motion detector system for a swimming pool includes a transducer responsive to positive and negative pressure changes in swimming pool water and operative to generate corresponding electrical signals. Comparators are responsive to the electrical signals, and operative to generate a crest signal while the positive pressure exceeds a predetermined positive threshold level, and a trough signal while the negative pressure exceeds a predetermined negative threshold level. A band pass filter prevents electrical signals having a frequency greater than a predetermined upper frequency, and lower than a predetermined lower frequency from passing from the transducer to the comparators. A pulse width discriminator is responsive to the crest signal and the trough signal and is operative to generate a qualified crest signal if the crest signal remains active for a first predetermined time interval, and a qualified trough signal if the trough signal remains active for a second predetermined time interval.