The river water quality in Malaysia has been monitored by the Malaysian Department of Environment (DOE). The Water Quality Index (WQI) used to appraise the river water quality is based on 6 parameters that are Dissolved oxygen, Biochemical Oxygen Demand, Chemical Oxygen Demand, Ammoniacal Nitrogen (NH3N), Suspended solids (SS) and pH. According to Malaysia Environment Quality Report 2004, a total of 926 water quality monitoring stations located within 120 river basins were monitored. The overall results in terms of river basin water quality showed 58 river basins (48.3%) were found clean, 53 river basins (44.1%) slightly polluted and 9 river basins (7.5%) polluted. The river basin water quality trend for the period of 1990 – 2004 is shown in the Figure 2.
Figure 2: River Basins Water Quality Trend, 1990-2004The major pollution sources in Malaysia are Biochemical Oxygen Demand (BOD), ammoniacal-nitrogen and suspended solids. The status of water quality in relation to these major pollution sources for the period of 1998 – 2004 are given in Figure 3, Figure 4 & Figure 5. High BOD is contributed by untreated or partially treated sewage and discharges from agro-based and manufacturing industries. The main source of ammoniacal nitrogen was sewage which include livestock farming and domestic sewage while the sources of suspended solids were earthwork and land-clearing.
Figure 3: River Basins Water Quality Trend (BOD), 1998-2004 
Figure 4: River Basins Water Quality Trend (NH3-N), 1998-2004 
Figure 5: River Basins Water Quality Trend (Suspended Solids), 1998-2004 
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