Abstract: We integrated a dynamic hydraulic model, the Hydrologic Engineering Centers River Analysis System (HEC-RAS), with a dissolved oxygen (DO) model to (1) investigate DO dynamics, and (2) evaluate the applicability and performance of an oxygen enhancement device (ESWED) in the field. We executed the study in the Hwajiang wetland, a highly polluted, tidally influenced freshwater marsh in northern Taiwan. This one-dimensional integrated model solves hydrodynamics with mass balance equations to simulate DO dynamics driven by rates of atmospheric oxygen exchange and biochemical processes. It specifically considers the coupled impacts of semi-diurnal tidal-induced hydraulic variations, temperature, channel slope, and wind velocity on DO. However, ESWED can only increase DO by an average of 0.62 mg L−1 at 1 m downstream, but cannot raise DO from anoxic (0 mg L−1) to hypoxic (<2 mg L−1). Nonetheless, the fundamental way to improve DO levels is to ensure continuous circulation of water flow. As a result, we recommend that decreasing sources of pollutants and increasing water discharge remain the most effective and sustainable solutions to prevent hypoxia and anoxia.