Even before Gen. George Washington ordered some of his soldiers onto armed schooners to attack British shipping, his men were venturing into the waters that nearly surrounded and protected Boston. The Continentals made raids in whaleboats, attacked enemy positions from floating batteries, and, as shown in this oft-quoted extract from his general orders for 22 Aug 1775, used the Charles River for bathing and recreation:
The General does not mean to discourage the practice of bathing whilst the weather is warm enough to continue it, but he expressly forbids any person’s doing it at or near the bridge in Cambridge, where it has been observed and complained of that many men, lost to all sense of decency and common modesty, are running about naked upon the bridge, while passengers, and even ladies of the first fashion in the neighborhood, are passing over it, as if they meant to glory in their shame. The guard and sentries at the bridge are to put a stop to this practice, for the future.New England can get hot in August.
This map from one of the National Park Service’s Bunker Hill lesson plans shows how close the bridge was to the center of Cambridge and the college. The Anderson Memorial (a.k.a. “Larz Anderson”) Bridge spans the same place now.