A dynamic hydrologic model was developed for the Örtülüakar Marsh in Turkey to investigate the causes of water-level decreases observed since the 1990s and to explore potential remediation and sustainability options. Örtülüakar Marsh is a sub-system of the Sultan Marshes ecosystem, a large wetland complex consisting of freshwater marshes and salt-water lakes in the Develi Basin of south-central Turkey. The wetland has experienced significant seasonal and long-term water-level changes after the construction of an irrigation project in the catchment. The model uses a monthly time scale and solves the unsteady water-balance equation. Inputs from precipitation, overland flow, springs and ground water, and outputs due to evapotranspiration and surface flow are represented in the model. The model was calibrated to fit monthly water-level measurements from 1997 to 2003. Sensitivity analyses showed that the model is highly sensitive to evapotranspiration and ground-water inflow. Simulations of several water allocation options suggest that ground-water use should be reduced in the Develi Basin to halt the decline in water level in the Örtülüakar Marsh.