The Kaoping River basin is the largest and the most intensively used river basin in Taiwan. It is 171 km long, drains a catchment of more than 3,257 km2, and has a mean flow of 239 m3/s. It serves as a water supply to the Kaohsiung City (the second largest city in Taiwan), several towns, two counties, and a number of large industries (electronic, steel, petrochemical, etc.). Although the mean annual rainfall in this river basin is close to 3,000 mm, over 90% of which appears in the wet season. The period of high flow rate in the stream usually occurs in the late spring and summer due to the impacts of monsoon and typhoon. Non-Point Sources (NPS) pollutants, which are associated with stormwater runoff from agricultural land uses can be quite diffuse and difficult to treat. In this study, land use identification in the basin was performed by properly integrating the skills of geographic information system (GIS) and global positioning system (GPS). Remote sensing image and Digital Elevation Model (DEM) of Kaoping River Basin were applied for the land use identification task. An integrated watershed management model (IWMM) was applied for simulating the water quality and evaluating NPS pollutant loads to the Kaoping River. The watershed was divided into catchments and river segments. The land use patterns were defined by the surface coverage of each catchment. The underneath soil can have several layers, and each land use has its vegetation characteristic and erosion coefficient. The model was calibrated and verified with field data from water quality monitoring stations. The calibrated model was used to develop best management practices (BMP). Moreover, the Water Quality Analysis Simulation Program (WASP) was also applied for the water quality simulation. The model was calibrated and verified with water quality data, and the model was used to analyze the impacts of NPS loading on water quality. The major objectives of this study were to (1) investigate and identify the current contributions of NPS pollutants to the Kaoping River pollution, (2) perform the land use identification and construct the watershed GIS to effectively manage the watershed, (3) perform water quality and soils sampling and analyses, (4) apply multimedia models for NPS pollution evaluation and water quality simulation, and (5) evaluate the effectiveness of the applied remedial strategies on watershed management and water quality improvement. This study identified major land-use patterns in Kaoping River Basin using SPOT images and GIS/GPS/RS techniques. The major findings from the GIS, field, and modeling tasks include the following: (1) Fourteen types of land-use patterns in the watershed area of the basin were classified with the aid of the Erdas Imagine process system; (2) Orchard gardens, rice paddies, sugarcane fields, betel palm farms, and tea gardens dominate the farmland areas in the basin and are scattered around on both sides of the river corridor; and (3) Simulated results indicate that NPS pollution plays a significant role in the deterioration of the downstream water quality of Kaoping River and caused a significant increase in suspended solids loads into the basin¡¦s water bodies. Concern about the deteriorating condition of the river led the Government of Taiwan to amend relevant legislation and strengthen the enforcement of discharge regulations to effectively manage the river and control pollution. Based on the results of this study, application of BMPs [e.g., source reduction, construction of grassy buffer zone, and land-use management] for NPS pollutant control are required. Multimedia modeling results indicate that the application of the following specific BMPs can reduce the effects of NPS suspended solids pollution on the water quality of Kaoping River: (1) Conversion of farmlands on hillsides of the upper catchment to forest; and (2) Conversion of rice paddies and agricultural lands to buffer zones (e.g., grassy strip, detention pond, and constructed wetland) along the riverbank areas of the three sub-basins. With application of these two proposed BMPs, the peak suspended solids concentrations in the wet seasons could be significantly reduced. Results and experience obtained from this study will be helpful in designing the watershed management strategies for other similar river basins.