Long-Reach Ethernet Passive Optical Networks (LR-EPONs) have become a promising broadband access technology due to cost-effectiveness and the ability to simplify Metropolitan Area Network (MAN) and Local Area Network (LAN) architectures. However, the increased propagation delay has led increased idle time for interleaved-based Dynamic Bandwidth Allocation schemes resulting in poor bandwidth utilization. This is because previously proposed DBA schemes used the conventional report-grant mechanism where the Optical Network Units (ONUs) report the required information to the Optical Line Terminal (OLT), and the OLT schedules and grants the transmissions after receiving this information. Conversely, since the LR-EPON is designed for covering a wider area, i.e., serving more end users, the bandwidth of single-channel LR-EPON is insufficient to accommodate the bandwidth demand of the increased number of the end users. Therefore, in order to resolve the above problems, the current study proposes a DBA scheme, namely ONU-based Decentralized DBA (OD-DBA) over a Wavelength Division Multiplexing (WDM) LR-EPON. In this scheduling scheme, the current study uses an Array Waveguide Grating (AWG) module to enable decentralized scheduling among all ONUs. In this manner, network utilization will not be restricted by the increased propagation delay. Finally, computer simulations are performed to compare with existing DBA schemes to verify the effectiveness and efficiency of the proposed OD-DBA scheme.