July 13, 2013 in Boston was a day more than 50 years in the making, as the long-suffering Charles River was opened for recreational swimming. Infamous for its heavy pollution, the river had become the butt of many a joke, and deservedly so. It sounds like jest to say that anyone who fell in the river was advised to go to the hospital for a tetanus shot, but that was exactly the case. After receiving a “D” grade for water quality by the U.S. EPA in 1995, the Charles began a steady road to recovery that resulted in a “B+” in 2011. And this summer, after half a century, it was once again open to swimmers — and swim they did.