The Charles River is about 80 miles in length. It starts in Hopkinton and winds its way to Boston Harbor. Between the railroad bridge and the Harvard Bridge, the water averages about fifteen feet in depth. Most of the river beyond the Harvard Bridge is shallow. Four miles upriver, the water is about three feet deep.

In 1614, John Smith explored the coast of New England, including Boston Harbor, and drew maps. Back in England, 15-year old Prince Charles (the future Charles I) was asked to give names to some of the geographic features. He named the river for himself.