Bristol County Beaches Cleanest in Massachusetts SouthCoast beaches are the cleanest in the state this year, according to a new report from the Environment Massachusetts Research and Policy Center. The center's 2021 Safe for Swimming report shows the results of testing 556 beaches in the state for fecal bacteria like E. coli. It revealed Bristol County has the lowest average percentage of days with potentially unsafe water of all eight seaside Massachusetts counties. Bristol County beaches were deemed potentially unsafe just 2% of the time on average, according to the center's data. This represents half the average of the next-best Dukes County, covering Martha's Vineyard and the Elizabeth Islands.