Water quality impairment in agricultural watershed is a major environmental concern in the United States and elsewhere. Identification of critical water quality areas across a watershed is necessary to locate target areas for the implementation of Best Management Practices and nonpoint source pollution control. In order to identify critical water quality areas in the 234,400-acre Bayou Plaquemine Brule watershed, we monitored water quality from April 2002 to March 2007 in seven locations- four at the main channel and three at the tributaries of the Bayou Plaquemine Brule. The Bayou Plaquemine Brule watershed has been included in Louisiana's 303(d) list of impaired bodies for several years. Dissolved Oxygen (DO), temperature, conductivity, pH, and turbidity were monitored in Bayou Plaquemine Brule Watershed from April 2002 to March 2007. Grab samples were collected for laboratory determination of Total Nitrogen, Total Phosphorus (TP), Nitrate/Nitrite-N, 5-day Biological Oxygen Demand (BOD5), Total Suspended Solids (TSS), and Soluble Reactive Phosphate from October 2002 to September 2006. Results indicated that critical water quality areas exist in the watershed. Downstream of the Bayou Plaquemine Brule has depleted DO levels, while upstream had insufficient flows especially during the summer months. The Cole Gully sub-watershed has elevated TSS, and the Bayou Wickoff sub-watershed has elevated BOD5. Excessive littering was observed in the Bayou, especially in the middle section of the watershed.