An experimental investigation has been made to detect cavitation in a pump–storage hydropower plant prototype suffering from leading edge cavitation in pump mode. Vibrations and acoustic emission on the housing of the turbine bearing and pressure fluctuations in the draft tube were measured and the corresponding signals were recorded and analyzed. The analysis was based on the analysis of high-frequency content of measured variables. The pump–storage hydropower plant prototype has been operated at various input loads and Thoma numbers. Several estimators of cavitation were evaluated according to a coefficient of determination between the Thoma number and cavitation estimators. The best results were achieved with a compound discharge coefficient cavitation estimator that is based on the discharge coefficient and several rms estimators: vibrations, acoustic emission, and pressure fluctuations. The compound discharge estimator was set as a product of the rms estimator and the squared discharge coefficient. Cavitation estimators were evaluated in several intervals of frequencies; the best frequency interval for the vibration sensor on the turbine cover was from 24 to 26 kHz, for the vibration sensor on the guide vane 36–40 kHz, for the acoustic emission sensor on the turbine cover 140–145 kHz, and for the pressure fluctuation sensor in the draft tube wall 130–150 kHz.