This work assessed the impacts of land-use patterns in the Ruvu river basin on water quality in the river system. Seasonal changes in water quality parameters were also investigated. Ten river water-sampling stations were selected and samples were collected and analysed according to standard analytical procedures. The results showed that physico-chemical parameters of river water ranged as follows: pH, from 6.95 ± 0.09 to 8.07 ± 0.23; temperature, from 14.0 ± 0.06 to 31.1 ± 0.4 °C; EC, from 39.8 ± 0.8 to 48,734 306 μs/cm; TDS, from 19.9 ± 0.4 to 24,367 ± 152.9 mg/l; turbidity, from 3.0 ± 0.6 to 840 ± 69.3 NTU and DO, from 6.8 ± 0.02 to 16.78 mg/l. The ranges for nutrient concentrations were NO3–N, from 0.006 ± 0.0003 to 0.62 ± 0.3 mg/l; NH4–N, from 0.34 ± 0.17 to 16.2 ± 0.5 mg/l; PO4–P, from 0.009 ± 0.001 to 1.75 ± 0.2 mg/l and TP, from 0.02 ± 0.003 to 3.56 ± 0.38 mg/l. Generally, water samples from stations with forested catchments had high levels of DO and low levels of NH4–N and NO3–N compared to those from farmland, industrial, residential and market places. There were clear seasonal variations showing an increase in the concentrations of nutrients during rainy season. The results show impairment of the water quality of the river by anthropogenic activities in the catchment. Water pollution prevention strategies to ensure prevention of pollution and protection of water resources in the Ruvu river watershed are recommended.