Most hydrodynamic vertical axis turbine concepts use solid blades with active adjustable pitch. These turbines generally need external starting or active pitching mechanisms to overcome their limited starting performance. In this study, a simple and cost-effective vertical axis turbine with flexible foils was designed based on inspiration from hydrodynamic thrust characteristics of aquatic creatures. A full-scale turbine was tested in a controlled river environment in Norway. The turbine’s high solidity, flexible foils with self-adjustable cambering, and pivot and spring arrangements on the blade and arm connections enabled the following: reduced turbine vibrations, dynamic foil adjustments, a passive blade pitch action, and limited variation in rotational speed versus incoming flow velocity. These novel aspects resulted in a high performance turbine that attained up to a 0.37 power coefficient in a confined channel and could self-start at low inflow water velocities.