Irrigators are frequently accused of causing a deterioration of water quality in the Murray Darting Basin. For many catchments, such as the Gwydir in Northwest NSW, little reliable information is available to assess the impact of irrigation on water quality. The aim of this research is to measure the water quality (in terms of sediment, salts and nutrients) of the Gwydir Valley Watercourses. By monitoring water quality above, within and below the irrigation area, any changes in water quality within the irrigation area can be examined to determine the impact of irrigation. Water quality data was also combined with river now data to determine the quantity (load) of sediments, salts and nutrients that may leave the Gwydir Valley and enter the Murray Darting Basin.