This study employed different indices, namely the weighted arithmetic water quality index (WQI), Carlson Trophic State Index (TSI), van Ginkel TSI, and Trophic Level Index (TLI) to determine the water quality status of a man-made dam for the needs of sustainable water resource management in Southern Africa. The selection of indices for the study was based on the impacts of anthropogenic activities on the dam. The Roodeplaat Dam exhibited the spatial variation of physicochemical characteristics, indicative of influence by point-source pollution. Although the dam was classified as being eutro-hypertrophic, it was evident that water clarity was not a limiting factor but was P-limited, which was an indication of limiting conditions on primary production. Moreover, the WQI calculated for the dam with an average of 93.94 demonstrated very poor water quality that could be used for crop irrigation purposes only. As such, continued nutrient enrichment must be mitigated to sustain fitness for irrigation, at least. However, strategic goals should involve widening fitness for use. The selected indices were found to be effective for water resource management and could be applied to dams impacted by point-source pollution in Southern Africa. Thus, this study recommends the implementation of an integrated management approach, which needs to prioritize nutrient management to retain societal resource value.

Anthropogenic activities significantly threaten aquatic ecosystems, accelerating water quality deterioration through pollution, overexploitation, and habitat disturbance. Roodeplaat Dam in South Africa exemplifies these challenges, experiencing nutrient overload driven by malfunctioning wastewater treatment works (WWTWs), urban runoff, and agricultural activities. This study investigates the spatio–temporal dynamics of flow patterns and nutrient loads in Roodeplaat Dam, focusing on the interplay between nutrient pollution, land use, and land cover change (LULCC). A multi-site sampling approach was employed to assess total phosphorus (TP) and nitrate–nitrite (NO₃ + NO₂) loading, complemented by geospatial analysis of LULCC impacts over two decades. The study revealed that TP and NO₃ + NO₂ concentrations surpassed permissible limits at certain monitoring sites, particularly downstream of WWTWs during low-flow periods, demonstrating their substantial role in elevating nutrient levels. The study further revealed that extensive human-driven changes in the catchment area were key contributors to nutrient dynamics. These changes included a reduction in vegetation cover from 65% to 45.17%, an increase in soil exposure from 10.25% to 22.01%, and urban expansion from 26.56% to 32.32%. These alterations disrupt natural nutrient cycles, leading to increased runoff and potential eutrophication of water bodies. Thus, to address these challenges, this study underscores the need for an integrated strategy that combines nature-based solutions, enhanced wastewater treatment, stricter regulatory compliance, and adaptive management to mitigate pollution and improve water resource sustainability. The insights gained from this case study provide valuable guidance for managing similar systems in developing regions under increasing anthropogenic and climatic pressures.

Poorly treated domestic wastewater and diffuse nutrient loading from agriculture and informal human settlements greatly threaten water resources due to the alteration of ecosystem function and the reduction of the water’s fitness for use. Thus, the aim of the study was to assess nutrient loading in the eutrophic Roodeplaat Dam (RD) to inform water resource management as a foundation for the rehabilitation of the dam. The objectives were to determine Total Phosphorus (TP) and Nitrogen (N) loading capacity into the RD as well as to propose a total mean annual nutrient reduction for the sustainability of the dam. Flow Duration Curves and Load Duration Curves were employed as analytical tools. It was observed from the study N and TP varied significantly among the sites investigated and the actual TP loads were significantly higher than the allowable load throughout the study area. The study further observed that nutrient loading was more prominent during low flows due to the reduced dilution effect. Thus, this study recommended the application of nature-based solutions to control pollution and reduce stormwater and runoff input, as well as employing low-cost green treatment technology options to reduce nutrient loads from domestic wastewater effluent in municipal wastewater treatment pond systems, which requires less energy. Stringent point source pollution control measures were further recommended, and that water quality planning should consider the desired beneficial water use per catchment, considering the impactors.