The Governments of Canada and the United States are committed to providing public access to environmental information about the Great Lakes basin ecosystem through the State of the Great Lakes reporting process. The work is undertaken in accordance with the Great Lakes Water Quality Agreement, and is integral to the mission to restore and maintain the chemical, physical and biological integrity of the waters of the Great Lakes basin ecosystem. Knowing the environmental condition of the Great Lakes can allow for effective decision-making by all Great Lakes stakeholders. The information in this report, State of the Great Lakes 2009, has been assembled from various sources with the participation of many people from throughout the Great Lakes scientific community. The data are based on indicator reports and presentations from the State of the Lakes Ecosystem Conference (SOLEC), held in Niagara Falls, Ontario, October 22-23, 2008.