Proper assessment of water quality status in a river system based on limited observations is an essential task for
meeting the goals of environmental management. Various classification methods have been used for estimating the changing
status and usability of surface water in River basin. However, a discrepancy frequently arises from the lack of a clear
distinction between each water utilization mode, the uncertainty in the quality criteria of water employed and vagueness or
fuzziness embedded in the decision making output values. Owing to inherent imprecision, difficulties always exist in
some conventional methologies like water quality index (WQI) when describing integrated water quality conditions with
respect to various chemical constituents, biological aspects, nutrients, and aesthetic qualities. In recent years, the fuzzy
logic based methods have demonstrated to be appropriated to address uncertainty and subjectivity in environmental issues.
In the present study, a methodology based on fuzzy inference systems (FIS) to assess water quality is proposed. This paper
presents a comparative study using fuzzy logic technique to assess status of river water quality by comparing the output
generated by fuzzy with that of conventional methods. The model is based on observations made from Semenyih
River in West Malaysia. The findings clearly indicate that the fuzzy inference system (FIS) may successfully harmonize
inherent discrepancies and interpret complex conditions. This river water quality model can be extended to determine the
non-regulated contaminants in water.