In 2007, the number of river basin monitored was reduced from 146 to 143. This was due to the merging of three (3) river basins which are located close to each other. It was found that Lembangan Linggi in Malacca is actually linked to Lembangan Linggi in Negeri Sembilan; Lembangan Pontian in Johor merged with Lembangan Rompin before flowing to the sea; and Lembangan Semerak in Kelantan is integrated with Lembangan Kemasin. Thus, Lembangan Linggi in Malacca, Lembangan Pontian and Lembangan Semerak were excluded resulting in 143 river basins. However the number of monitoring stations remains at 1,064.
Out of these 1,064 monitoring stations, 638 (60%) were found to be clean, 376 (35%) slightly polluted and 50 (5%) polluted. There was a significant improvement in the river water quality in 2007 compared with 2006. The number of clean river basins was 91 (64%) compared to 80 in 2006 and the number of slightly polluted rivers basin dropped from 59 in 2006 to 45 (31%) in 2007. However, the number of polluted river basin remains at 7 (5%).
As in previous year the major pollutants detected were Biochemical Oxygen Demand (BOD), Ammoniacal Nitrogen (NH3-N) and Suspended Solids (SS). In line with the overall improvement in river water quality in 2007, the number or river basins polluted by BOD decreased from 22 in 2006 to 12 in 2007 and the number of river basins polluted by NH3-N decreased from 42 to 36 but the number of river basins polluted by SS remain at 42.. High BOD can be contributed to untreated or partially treated sewage and discharges from agro-based and manufacturing industries. The main sources of NH3-N were domestic sewage and livestock farming, while the sources for SS were mostly earthworks and land clearing activities.