A 3-dimensional regional hydrodynamic and eutrophication model was set up for the Ho Bay, Graadyb Estuary. The model was based on MIKE 3 FM, DHI's flexible mesh model system, extended with the ECOLab biogeochemical process module. The model was calibrated using level- and current data from a campaign in 2004, and the eutriphication model calibrated using Ribe County's monitoring data from 2001. The influx of nitrate bearing groundwater was estimated during WP 5, mainly covering the NE coast of Ho Bay. Simulations with and without influx of groundwater were made for the spring 2001 period. Comparison of the results showed that the influence of the nitrate bearing groundwater is relatively small, at most 0.5% on selected water quality parameters. The minor effect is explained by the relatively small contribution to the total nutrient input to the estuary and the relatively efficient tidal flushing of the estuary.