Environmental impactWater reservoirs are the primary source of freshwater for most cities around the world, yet the general point-based approaches are usually insufficient to identify the spatiotemporal variations of reservoir water quality. We develop an effective and reliable approach for mapping the water contents of Chlorophyll-aand suspended solids for the entire Tsengwen Reservoir at intervals of about one month in 2006. This support comes from the multi-temporal observations made by Formosat-2 that are difficult to attain with other space-borne platforms. This research encourages the applications of Formosat-2 high spatiotemporal imagery on monitoring a multi-lake ecological system and relating the water quality to the watershed management practices. This research would motivate the environmental community to explore the possibility of monitoring the environment from the daily revisit platform.