This study investigated the changes caused by diverting water applications at the riverhead of the Onchun Stream via the monitoring of several water quality and biological parameters between 10/09 and 10/10. The analysis indicated that the Onchun Stream distinctly decreased in terms of several water quality parameters, such as BOD, COD, TN, TP, and the concentration of heavy metals as compared to similar values in 2005, before the flowing of the Nakdong River. Especially, BOD showed the 2nd grade of water quality, with an average of 2.0 mg/l at all sites. The species number and standing crops of plankton and benthic macroinvertebrates in the Onchun Stream were also increased. Thus, it was concluded that diverting water from the Nakdong River to the Onchun Stream dramatically improved various environmental indices, such as water quality and biological changes.