Here, ultrathin, flexible, and sustainable nanofiber-based piezoelectric nanogenerators (NF-PENGs) are fabricated and applied as wave energy harvesters. The NF-PENGs are composed of poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) nanofibers with embedded barium strontium titanate (BaSrTiO3) nanoparticles, which are fabricated by using facile, scalable, and cost-effective fiber-forming methods, including electrospinning and solution blowing. The inclusion of ferroelectric BaSrTiO3 nanoparticles inside the electrospun P(VDF-TrFE) nanofibers enhances the sustainability of the NF-PENGs and results in unique flexoelectricity-enhanced piezoelectric nanofibers. Not only do these NF-PENGs yield a superior performance compared to the previously reported NF-PENGs, but they also exhibit an outstanding durability in terms of mechanical properties and cyclability. Furthermore, a new theoretical estimate of the energy harvesting efficiency from the water waves is introduced here, which can also be employed in future studies associated with various nanogenerators, including PENGs and triboelectric nanogenerators.