###### Abstract  
Surface water quality assessment is an important component of environmental protection and sustainable development. In this study, 24 sampling sites were arranged in the Wanquan River area of Hainan Island, China, in 2021, and nine water quality indicators were measured. The water quality of the Wanquan River was assessed using the single factor pollution index method and the Nemerow pollution index method; the spatial distribution characteristics of pollutants were revealed, and the sources of pollution were further analyzed using factor analysis. The results show that the overall water quality of the Wanquan River basin is good, with the average values of all indicators meeting China's Class III water quality standards. The results of the single factor pollution index method showed that 29% of the sampling sites were in the no pollution class, 38% in the slight pollution class, 25% in the light pollution class, and 8% in the moderate pollution class. The results of the Nemerow pollution index showed that 25% of the sampling sites were in the clean category, 17% in the cleaner category, 42% in the light category, and 17% in the moderate category. The results of the factor analysis show that agricultural activities and domestic sewage discharge are the main sources of pollution, with nitrogen and phosphorus being the most important factors affecting water quality. This paper proposes several measures to reduce water pollution in the Wanquan River, including improving agricultural activities, improving wastewater treatment, and strengthening environmental monitoring. The findings have practical implications for reducing water pollution in rivers and lakes and can provide a reference for policy decisions related to water resource management and environmental protection. W 202  
quality condition of rivers. The single factor evaluation method is widely used in many regions [18; 22] due to its ease of use, and it is the calculation method used in China's Environmental Quality Standards for Surface Water. The Nemerow composite pollution index method also has the advantages of simple calculation and conceptual clarity, as well as better accuracy in the evaluation results, and it is widely used in the field of water quality assessment [12; 23]. In this study, the single factor evaluation method and the Nemerow integrated pollution index method were selected to scientifically evaluate the water quality condition of the Wanquan River. The Wanquan River is the \"mother river\" of Hainan Island and is an important source of water for local people's livelihoods. Its water quality is directly related to the health and quality of life of the local people. At the same time, the Wanquan River also has an important regulatory role in the local ecosystem, and the deterioration of water quality can lead to the destruction of the local ecosystem, resulting in a reduction in biodiversity. However, little research has been conducted on the pollution status of the Wanquan River, and existing studies mainly focus on the analysis and evaluation of water quality indicators [24; 25]. The analysis of pollution sources is still lacking. Therefore, it is important to carry out a water quality assessment of the Wanquan River Basin for local environmental management and ecological protection. Based on the data from 24 sampling points of the Wanquan River in August 2021, this paper evaluates the water quality condition of the river and analyzes the pollution sources by using the single factor evaluation method, the Nemerow index method, and the factor analysis method. It is worth mentioning that this study introduces geostatistical methods to spatially interpolate the water quality indicators of the Wanquan River to further explore the correlation between water quality indicator data and geographic elements such as towns, traffic, and topography so as to better analyze the spatial distribution characteristics of pollutants and determine the sources of pollution.