The concentrations of four artificial sweeteners, acesulfame, saccharin, cyclamate, and sucralose, were measured at 23 sites along the length of the Grand River in southern Ontario, Canada, to evaluate the effectiveness of artificial sweeteners as tracers of domestic wastewater in the environment. River water was collected and analyzed from sampling campaigns that occurred in June and September 2007 and April 2009. The Grand River receives effluent from 30 municipal wastewater treatment plants, servicing a population of approximately 800,000 people at the time of this study. Due to their widespread use in consumer products, the fact that they are not metabolized in the body, and that they are resistance to degradation in wastewater treatment systems, high concentrations of all four artificial sweeteners were found in the Grand River. For three of the sweeteners, the maximum concentrations found at the time were the highest on record for a river anywhere in the world. Detailed information on the collection and