Water Quality Index (WQI) attempts to provide a mechanism for presenting a cumulatively derived, numerical expression defining a certain level of water quality [6]. In Malaysia according to Malaysian National Water Quality Standards (NWQS) the WQI comprises of six parameters which are highlighted in the following formula, however, different standards consider more parameters such as phosphorus, heavy metals, etc.The WQI and its major sub indexes (BOD5, NH3-N and TSS) trend for Linggi and Melaka catchments were plotted graphically to find out the most polluted river tributaries within the catchment for the time frame. The formula to obtain WQI is as follows: