The Klang River originates from the northern part of Selangor, drains the Klang Valley, and finally discharges itself into the Straits of Malacca, approximately 120 km away from the upstream point. As the state of Selangor and the city of Kuala Lumpur are going through tremendous development, the river is subjected to pollution from point and non-point sources. The pollution sources may come from urban activities, agricultural activities, industrial and commercial activities, and residential areas. In addition to this, the pollution loading from non-point sources is usually difficult to estimate because it is a function of rainfall/storm water runoff. The purpose of this research is to set-up a digitized model of the Klang Valley river basin to study the effect of development on the river basin by using computer modeling. In this paper, the used of GIS technique in determining the spatial variability in river basin has been explored. Based on the GIS technique, the DEM of the study basin was used to delineate the stream network and extract information of catchments characteristics. The locations of the point and non-point sources were surveyed and digitized spatially along the river basin. These are important as it will serve as a database before the water quality simulation can be performed. The developed model can also be extended to a larger basin. Field survey and further investigations would be helpful in calibrating the critical parameters and thus improving performance of the developed model.