Citation: Sakke, N.; Jafar, A.; Dollah, R.; Asis, A.H.B.; Mapa, M.T.; Abas, A. Water Quality Index (WQI) Analysis as an Indicator of Ecosystem Health in an Urban River Basin on Borneo Island. Water 2023, 15, 2717. https:// doi.org/10.3390/w15152717 Academic Editors: Mohd Khairul Amri Kamarudin and Mohd Ekhwan Toriman Received: 14 June 2023 Revised: 5 July 2023 Accepted: 12 July 2023 Published: 27 July 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). water Article Water Quality Index (WQI) Analysis as an Indicator of Ecosystem Health in an Urban River Basin on Borneo Island Nordin Sakke 1 , Adi Jafar 1 , Ramli Dollah 1, * , Abdul Hair Beddu Asis 2 , Mohammad Tahir Mapa 1 and Azlan Abas 3 1 Faculty of Social Sciences and Humanities, Universiti Malaysia Sabah, Kota Kinabalu 88400, Sabah, Malaysia; dinums@ums.edu.my (N.S.); adi.jafar@ums.edu.my (A.J.); herma@ums.edu.my (M.T.M.) 2 Centre for the Promotion of Knowledge and Language Learning, Universiti Malaysia Sabah, Kota Kinabalu 88400, Sabah, Malaysia; khairasis@ums.edu.my 3 Centre for Research in Development, Social and Environment (SEEDS), Faculty of Social Sciences and Humanities, Universiti Kebangsaan Malaysia, Bangi 43600, Selangor, Malaysia; azlanabas@ukm.edu.my * Correspondence: ramlid@ums.edu.my Abstract: The health of the river basin is characterised by its ecosystem health to provide significant and valuable resources and services for human use and the basin itself. However, the development of urban space and the intensification of human activities surrounding the river ecosystem have greatly disturbed the river’s health, thereby impacting human and environment. Therefore, this paper seeks to assess the degree of quality and cleanliness of river water, which is one of the river basin’s health indicators. To identify the issues that affect the river’s health, water quality indicators are used. The Inanam–Likas River Basin has been chosen due to its location within an urban area. Water quality data from 2014 to 2018 were analysed using the Water Quality Index (WQI) developed by the DOE. In addition, the Mann–Kendall test is also used to observe the trend and direction of the river’s health using WQI data from 1999 to 2019. Based on the analysis, the health of the river basin is moderately polluted due to land clearing and domestic sewage activities. This is shown by the relatively high percentage frequency of contaminated levels of WQI SS and NH3-N. The health level of the river in the upper course is better than in the lower course. This is because development and human activities are more concentrated in the lower course area compared to the upper course. Although the river’s health is currently at a moderate level, the trend indicates that its health is improving. Keywords: hydrology; drainage basin management; river pollution; Inanam–Likas River Basin 1. Introduction Urban rivers play an important role in maintaining the health of urban ecosystems. River basins provide significant resources [1] and are of great value to humans [2]. Urban river basins provide valuable ecosystem services, including heat reduction, flood control, recreational areas [3–5], small-scale or recreational fishing, sources of building materials (e.g., sand, gravel), and water for irrigation and household uses [6–8]. They also exhibit clear heat mitigation and cooling effects [9] and have the potential to serve as an important alternative water source [10]. Therefore, many cities worldwide are located in close prox- imity to or alongside rivers due to the abundance of water and the various resources they offer, such as transportation, food, and electricity [11]. The valuable ecosystem services provided by urban rivers, particularly the provision of clean water, contribute to creating liveable urban spaces and promising better lives for people. Currently, approximately 56% of the world’s population, totalling 4.4 billion inhabitants, resides in cities. This trend is projected to persist, with the urban population anticipated to more than double its current size by 2050. By that time, nearly 7 out of 10 people will be living in urban areas. Water quality poses as one of the primary challenges societies will encounter in the 21st century. It poses threats to human health, restricts food production, diminishes ecosystem functions, Water 2023, 15, 2717. https://doi.org/10.3390/w15152717 https://www.mdpi.com/journal/water