• The Huron River drains portions of seven counties in southeast Michigan. The Huron River Watershed is more than 900 square miles and consists of hundreds of tributary creeks, lakes, and the Huron River proper. The Michigan Department of Environmental Quality (MDEQ) began sampling intensively on the Huron River due to the city of Ann Arbor detecting per- and polyfluoroalkyl substances (PFAS) in the Huron River, which is the main source of the city of Ann Arbor’s drinking water, and the discovery of perfluorooctanesulfonic acid (PFOS) in the river at levels over the Rule 57 water quality standard of 11 ppt PFOS. The following is a timeline of PFAS investigation activities in the Huron River Watershed.