The Washington Aqueduct draws water from the Potomac River at a site just north of Great Falls. Engineers constructed a low weir, or underwater dam, across most of the width of the Potomac at this point to divert the force of the river's flow into the large intake pipes at the beginning of the aqueduct. Most of the river continues over the weir, flowing down over the limestone formations at Great Falls.
The path of the aqueduct loosely parallels the path of the C&O Canal, slightly upslope from the river basin. Note how the land north of the canal is home to numerous streams that flow through small hollows to the Potomac below. As the aqueduct traverses this landscape, the workers had to dig tunnels or build bridges over the undulating land, as the aqueduct required a consistent but gentle slope downward toward the city for its entire length.