Escherichia coli (E. coli) are bacteria that indicate fecal contamination and potential human health risks from swimming or recreation in the water. E. coli present in the Sudbury, Assabet, and Concord Rivers indicate the presence of fecal matter from birds, rodents, pets, livestock, humans, and other warm-blooded animals. Under the Clean Water Act, the rivers should be clean enough for “recreation in and on the water.” In the United States, most swimming-associated diseases are caused by a variety of pathogens associated with fecal matter. Human fecal matter can enter river water in a variety of ways, including municipal wastewater discharges, failure of on-site septic systems, combined sewer overflows, discharge of sewage by boats, re-suspension of sediments, and rainfall and resulting surface runoff. Data collection for fecal bacteria will commence during Summer 2019.