Deteriorating water quality in urban areas has drawn wide interest in China. In our study, water quality was monitored monthly during December 2009-November 2011 from 16 sites located in a trans-urban river. The spatial pattern showed that the concentrations of EC, Ca²⁺, Mg²⁺, BOD₅, COD_cr, TP, and NH₄ ⁺-N were higher midstream and downstream than upstream, while measured pH and DO upstream were higher than measurements midstream and downstream. The temporal pattern showed that the concentrations of EC, TP, BOD₅, H₄ ⁺-N, Mg²⁺, and Ca²⁺ in the wet season were lower than in the dry season, while the concentrations of COD_cr in the wet season were higher than in the dry season. Receptor-based source apportionment revealed that most of the variables were influenced by domestic sewage, cropland, and woodland runoff pollution. Therefore, the best method to prevent water quality degradation is to manage the domestic sewage, cropland, and woodland runoff.