The Department of Environment (DOE ) has been conducting monitoring of river since 1978, primarily to establish baselines and to detect water quality changes in river water quality and has since been extended to identifying of pollution sources as well. A total of 1,064 manual stations located within 143 river basins through out Malaysia.
Water quality data were used to determine the water quality status weather in clean, slightly polluted or polluted category and to classify the rivers in Class I, II, III, IV or V based on Water Quality Index (WQI) and Interim National Water Quality Standards for Malaysia (INWQS) every year. Water Quality Index (WQI) is computed based on 6 main parameters:-
- Biochemical Oxygen Demand (BOD)
- Chemical Oxygen Demand (COD)
- Ammoniacal Nitrogen (NH3N)
- Dissolved Oxygen (DO)
- Suspended Solids (SS)
Other parameters such as heavy metals and bacteria would be measured according to site requirement.
In addition, 15 automatic water quality monitoring stations had been installed to monitor river quality changes on a continuous basis at Sg.Perai (Seberang Perai – Pulau Pinang), Sg. Perak (Perak), Sg. Selangor (Selangor), Sg. Jinjang (WPKL), Sg. Linggi (Negeri Sembilan), Sg. Melaka (Melaka), Sg. Skudai (Johor), Sg. Keratong (Pahang), Sg. Terengganu (Terengganu), Sg. Sarawak (Sarawak), Sg. Langat (Selangor), Sg. Labu (Negeri Sembilan), Sg. Putat (Melaka), Sg. Batang Benar (Negeri Sembilan) and Sg. Rajang (Sarawak).