This work adopts high-frequency inductive power transfer (HF-IPT) to design an efficient WPT system for low-power sensors and robots in a fresh water environment, and explores the effect of fresh water on coil coupling at different distances. The system configuration is composed of a load-independent Class-EF inverter, PCB coils and a Class-D rectifier with an available gap up to 100 mm. In the experiments, the prototype achieved a peak system efficiency of 66.5% with a power delivery of 8.3 W at a 4.5 cm air gap with a coupling coefficient of 0.1. In a fresh water environment, it still maintained Zero Voltage Switching (ZVS) condition with a gap varying from 4.5 cm to 10 cm, achieving a peak system efficiency of 56.1 % over a wide power range from 0 W to 6.0 W. This study provides design guidelines for employing HF-IPT for low-power energy transfer in fresh water and explores potential factors, including the impact of
waterproof enclosures on system performance. The experimental results demonstrate that the load-independent Class-EF inverter can maintain ZVS in fresh water at all distances larger than the designed point (4.5 cm) without any tuning, indicating this topology is a promising candidate for HF-IPT in fresh water