The application of hydroinformatics tools is restricted in developing countries due to the non-availability of the required data and information under local conditions. This paper presents the state of water quality of the city of Vientiane (capital of Lao PDR) before the extensive rectification of its drainage network and describes an approach and methodology for water quality modeling. This is done with respect to the application of a combined hydrodynamic/water quality model based on minimal input data and observations for model verification. It further evaluates options to improve the deteriorating water quality observed in the rectified channels associated with the absence of suitable wastewater treatment. Two pollutants associated with the enrichment of receiving water bodies by wastewaters, total-P and NH4-N, are modeled. The modelling study is carried out in three steps: dry weather flow simulation, wet weather flow simulation and nutrient modeling using MOUSE. The dry weather flow simulations are carried out to calibrate the model for hydraulic roughness coefficient, dispersion coefficient and travel time. The wet weather flow simulations analyze the effect on flooding of two channel states, namely unvegetated and vegetated conditions. Nutrient modeling therefore evaluates removal efficiency by the vegetation. Model results are compared with the observed data and recommendations are made with respect to the predicted effects of the water quality improvement schemes studied. In conclusion, the modeling approach herein presented can be applied for performance analyses of urban channels in the developing part of the world, where data are often limited.