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Freshwater channels within Thaksin University (Phatthalung Campus) flow through sequential reaches dominated by different aquatic plant communities: (1) a Leafy Bladderwort reach (Utricularia aurea Lour) (2) a lotus reach (Nelumbo sp.), and (3) a Yellow Velvet Leaf reach (Limnocharis flava). This study asked whether different plant communities measurably influence water quality along the same flow path and across seasonal hydrologic conditions. Water quality was measured at three zones within each plant reach—upstream (before entering the plant reach), midstream (within the plant reach), and downstream (after passing the plant reach)—during October 2025 (early rainy season), November 2025 (flood period), and January 2026 (cool/dry period). Five indicators were analyzed: dissolved oxygen (DO), electrical conductivity (EC), total dissolved solids (TDS), water temperature, and pH (n = 27 observations; 9 per plant community). One‑way ANOVA tested differences among plant communities and Bonferroni post hoc tests identified pairwise contrasts. Across all samples, DO ranged 5.5–9.5 mg/L; EC 89–210 µS/cm; TDS 27–104 mg/L; temperature 26.0–28.5 °C; and pH 5.15–7.78. Plant community significantly affected EC (F = 4.812, p = 0.017), TDS (F = 5.113, p = 0.014), and temperature (F = 6.117, p = 0.007), but not DO (p = 0.540) or pH (p = 0.838). Post hoc tests indicated that the Yellow Velvet Leaf reach had significantly higher EC and TDS than both the Leafy Bladderwort and lotus reaches (p < 0.05), and higher temperature than the Leafy Bladderwort reach (p < 0.01). Flow‑based percent change from upstream to downstream suggested that Leafy Bladderwort and lotus reaches more often reduced EC/TDS, while the Yellow Velvet Leaf reach frequently showed increases. These results support nature‑based water treatment planning by highlighting how different local plant communities can either improve or deteriorate key physicochemical indicators along a natural flow system.