<p>Influenced by the rapid pace of economic growth and urbanization, the ecological environment of urban rivers is exceptionally delicate. Despite their relatively small basin areas, small-to-medium rivers are abundant in highly urbanized areas, making their health status a matter of considerable importance that warrants thorough attention and in-depth research. Taking the Yangmei River in Guangzhou as a case study, this research conducted field investigations on environmental factors and macroinvertebrates. Biological indicator method and structural equation modeling (SEM) were employed to conduct health assessment and analyze the driving forces behind its health issues of the Yangmei River. The findings reveal that pollution tolerant species dominate the macroinvertebrates community in the Yangmei River. A rapid macroinvertebrate bioassessment index (RBI) comprising seven indicators was established. According to the RBI results, two sampling sections were identified as good, three as fair, and the remaining three as poor. Based on the redundancy analysis results, NO₂-N, TP, Cond, and Built-up land were identified as the primary factors influencing the distribution of macroinvertebrates in the Yangmei River. In terms of health assessment, considering SEM results and the water quality characteristics, it is concluded that high concentrations of nitrogen and phosphorus pollution are the driving forces behind the current health issues of the Yangmei River. This study not only provides strong data support for the health assessment and ecological governance of the Yangmei River but also offers references and theoretical guidance for the health assessment and ecological governance of small-to-medium rivers in other highly urbanized areas.</p>