Widely distributed across the globe, water wave energy is one of the most promising renewable energy sources, while little has been exploited due to various limitations of current technologies mainly relying on electromagnetic generator (EMG), especially its operation in irregular environment and low frequency (<5 Hz). The newly developed triboelectric nanogenerator (TENG) exhibits obvious advantages over EMG in harvesting energy from low-frequency water wave motions, and the network of TENGs was proposed as a potential approach toward large-scale blue energy harvesting. Here, a review is given for recent progress in blue energy harvesting using TENG technology, starting from a comparison between the EMG and the TENG both in physics and engineering design. The fundamental mechanism of nanogenerators is presented based on Maxwell's displacement current. Approaches of water wave energy harvesting by liquid-solid contact electrification TENG are introduced. For fully enclosed TENGs, the structural designs and performance optimizations are discussed, based on which the TENG network is proposed for large-scale blue energy harvesting from water waves. Furthermore, the energy harvested by TENG from various sources such as water wave, human motion and vibration etc, is not only new energy, but more importantly, the energy for the new era – the era of internet of things.