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Water quality monitoring is one of the most important pillars in water resource management. However, water quality monitoring can be resource intensive, especially for developing countries with limited resources. As such, Water Quality Indices (WQIs) are developed as a convenient tool to summarise general water quality into a single numerical value using a few water quality parameters. It helps to condense and communicate water quality information to policy-makers in an efficient way that could guide future water resource management. In addition, it is imperative to understand the influence of surrounding land use on water quality in order for effective water resource management to materialise. Water quality in Johor River is heavily influenced by surrounding land use within the Johor River Basin (JRB) in the state of Johor, Malaysia. In the recent years, there have been recurring reports of pollution in these rivers, which has generated concerns over the long-term sustainability of the water resources in the JRB. Specifically, this water resource is a shared commodity between two states, namely, Johor state of Malaysia and Singapore, a country located south of Johor. However, prior to this study, few research on the influence of land use configuration on water quality has been conducted in Johor. In addition, it is also unclear how point sources of pollution from wastewater treatment plants (WWTPs) influence water quality under different seasonality in the JRB. This study aims to develop a site-specific WQI for the Johor River Basin (JRB), Malaysia, and understand how external sources (i.e. land use and point sources) affect water quality. Water samples were collected from 49 sites within the JRB from March to December in 2019. Spatial analysis showed that the most polluted rivers were Chemangar, Lebam, and Tiram river, while Pelepah has the highest water quality as it consistently scored the highest WQI values across time.Results showed that influence from WWTPs on water quality was greater during the dry season, and less significant during the wet season. In particular, point source was highly positively correlated with ammoniacal-nitrogen (NH3-N). On the other hand, land use influence was greater than point source influence during the wet season.Residential and urban land use were important predictors for nutrients and organic vi matter (chemical oxygen demand); and forest land use were important sinks for heavy metals but a significant source of manganese.

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