One of the most cost-effective and environmentally sound methods of developing hydropower is through the uprating of hydroelectric turbines. In many countries hydroelectric dams have turbines that are approaching their expected service life, with plans underway to install replacement turbines that are expected to improve fish passage survival. To validate these improvements, there is a need to develop a baseline hydraulic characterization of existing Kaplan turbines. An autonomous sensor device known as the Sensor Fish was deployed at Ice Harbor Dam to characterize the hydraulics under different operating conditions. Nadir pressures varied by operating condition, with values decreasing with operating power (144–106 kPaA). Pressure changes during turbine passage varied by operating condition, with values increasing with operating power (311–344 kPa). There were slightly more significant events (acceleration ≥95G) in the stay vane/wicket gate region than the runner region. Rotational velocity data were similar between operating conditions. Sensor Fish data amassed during field studies in similar turbines were used for comparison. This study offers critical insights into the biological performance of large Kaplan turbines and provides vital information that can be used to make informed decisions that lead to additional design or operational improvements. •Sensor Fish data collected in a large Kaplan turbine at Ice Harbor Dam.•Nadir pressure and rotational velocity were lowest among turbines compared.•Severe acceleration events were similar among the turbines compared.•Data provides insight into the biological performance of large Kaplan turbines.•Data provides information that can lead to further design/operational improvements.