Where Does a River Flow?


Potomac River, DC, MD, VA | © Robert Pos

Potomac River, DC, MD, VA | © Robert Pos

Have you ever wondered where a river comes from and where it flows?

The Department of Interior just released a new tool that lets you map out a river from its source in countless small headwater streams all the way downstream. All of our iconic rivers, from the Colorado to the Mississippi, start out as seemingly insignificant networks of small streams, seeps, wetlands, and rivulets.  There has been little comprehensive analysis of these networks, but the U.S. Geological Survey estimates that first and second-order streams (the very smallest) make up 75 percent of the total length of stream and river channels [PDF] across the country, although the actual number is likely much higher.

This becomes strikingly clear when you focus on some of the major rivers across the United States. For instance, this map highlighting the small streams and tributaries that make up the Mississippi River visually demonstrates the huge land area it covers (37 percent of the continental U.S).  To get a little closer to home, I did the same for the Potomac River. The Potomac is the source of my drinking water here in Washington, DC and I cross it twice a day on my commute to work.  Without including the smallest networks of seeps and rivulets, the tool shows that an estimated 3,355 stream miles make up the river from its source to its outlet in the Chesapeake Bay, crossing 36 counties in five states with a combined population of approximately 5 million people.

Why are small streams important?

This interactive tool helps to reveal the connections between small streams and wetlands and iconic rivers like the Mississippi. It is in small streams and wetlands where the greatest connections between land and water occur in ecological processes that can remove and store excess nutrients to protect water quality. Small streams help to buffer the impacts of floods [PDF] by absorbing and slowing down rainfall and snowmelt and play a critical role in groundwater recharge.

Unfortunately, protections for small streams and wetlands are no longer guaranteed. Following two Supreme Court decisions, protections for these waters was put into question. Although the Environmental Protection Agency and the Army Corps of Engineers are moving forward to clarify the scope of the Clean Water Act and restore protections for these critical waters, their efforts are consistently under attack in Congress. It’s critical that the Army Corps and the EPA are able to move forward with guidance or a rulemaking to clarify the scope of the Clean Water Act to restore protections to small streams and wetlands.

3 Responses to “Where Does a River Flow?”

Kimberly L. Lairson

Thanks for this river source tool. The Whitewater River runs through my town, and I am anxious to see what its source is.

Patti Carothers

This seems to be a helpful, informative & fun tool. I will use it in my dialog about the rivers as I lead my paddle trips – thank you!