Water quality indexes (WQI) were applied in the Tigris River using thirteen water quality parameters (pH, chlorides, sulfate, nitrate, salts, BOD5, iron, boron, zinc, lead, cadmium, copper, and chromium) in this study. They were calculated for the six years from 2008 to 2013, then compared with sets of standard values of rivers maintaining system. The results indicated that the water quality of the Tigris River for CCME-WQI was generally "Fair" to "Good" in 2008, 2009, and 2010 (CCME WQI range: 69.67 - 88.46) for all sites. CCME WQI values fell from "Marginal" to "Fair" in all sites over the last two years (2012 and 2013). WPI was " pure" to " Moderately polluted " from 2008-2011 (WPI range: 0.6-1.08) for all sites. Whereas, WPI values dropped to ranging from " Moderately polluted " to "polluted" (WPI range: 1.1-2.3) in all sites at 2012 and 2013. The effect of various human activities and dryness were evident on some parameters such as the heavy metals, Sulfate, Chlorides, Salts and Nitrate. Where their concentrations exceeded the permissible limits of the rivers maintaining system in most of the sites, and thus were the reason for the decline in the values of the indices. So, the monitoring of the Tigris River is important for proper management and for preserving this important water source.