This review summarizes the development of water-flow piezoelectric energy harvesting over the past 25 years. Piezoelectric energy harvesting from water flow is a promising technique for powering low-power electronic devices in water environments. The process involves three stages: energy extraction, energy conversion, and energy transfer. Energy extraction involves capturing mechanical energy from water flow using various excitation mechanisms such as vortex-induced vibration, galloping, wake-induced vibration, turbulence-induced vibration, cavity-flow-induced vibration, blocking, and wave motion. The extracted mechanical energy is then converted into electrical energy by piezoelectric materials, which are typically in the form of ceramics (e.g., PZT), macrofiber composites (MFCs), or polymers (e.g., PVDF). The conversion efficiency depends on the material's piezoelectric properties and the working mode (d33, d31, or d15). Finally, the electrical energy is transferred to an external load via an interface circuit. The review highlights the importance of optimizing the excitation mechanisms, piezoelectric materials, and energy transfer circuits to improve the performance of water-flow piezoelectric energy harvesters. It also discusses the challenges associated with these systems, including their sensitivity to environmental factors such as humidity and flow velocity, and proposes future research directions to enhance their efficiency and adaptability. The review emphasizes the potential of piezoelectric energy harvesting for remote power supply in water environments, particularly for low-speed flows such as rivers and the ocean.This review summarizes the development of water-flow piezoelectric energy harvesting over the past 25 years. Piezoelectric energy harvesting from water flow is a promising technique for powering low-power electronic devices in water environments. The process involves three stages: energy extraction, energy conversion, and energy transfer. Energy extraction involves capturing mechanical energy from water flow using various excitation mechanisms such as vortex-induced vibration, galloping, wake-induced vibration, turbulence-induced vibration, cavity-flow-induced vibration, blocking, and wave motion. The extracted mechanical energy is then converted into electrical energy by piezoelectric materials, which are typically in the form of ceramics (e.g., PZT), macrofiber composites (MFCs), or polymers (e.g., PVDF). The conversion efficiency depends on the material's piezoelectric properties and the working mode (d33, d31, or d15). Finally, the electrical energy is transferred to an external load via an interface circuit. The review highlights the importance of optimizing the excitation mechanisms, piezoelectric materials, and energy transfer circuits to improve the performance of water-flow piezoelectric energy harvesters. It also discusses the challenges associated with these systems, including their sensitivity to environmental factors such as humidity and flow velocity, and proposes future research directions to enhance their efficiency and adaptability. The review emphasizes the potential of piezoelectric energy harvesting for remote power supply in water environments, particularly for low-speed flows such as rivers and the ocean.