Water, Water—And Watersheds—Everywhere

We explore Baltimore City's watersheds and subwatersheds in this story series. In the first installment, we answer a central question: So, what is a watershed anyway?

  • Conservation

If you ask a Baltimorean what watershed they live in, there's one answer you're likely to get, and for good reason! The Chesapeake Bay—the largest estuary in the United States, with more than half of its 200 miles located within the state of Maryland—is top of mind for many locals.

More than 150 major rivers and streams drain into the Chesapeake Bay, a big, beating heart fed by smaller streams and creeks that branch out like major arteries and small, ribbon-like veins into five states beyond Maryland—New York, Pennsylvania, West Virginia, Delaware and Virginia—as well as Washington, D.C. The entire Chesapeake Bay watershed spans 64,000 square miles and encompasses everything from forests and farms to cities and suburbs. The area is also home to more than 18 million people.

Aerial View of Wetlands and Trees in the Blackwater Wildlife Refuge on Maryland's Eastern Shore.

The Chesapeake Bay is not the largest watershed in the country, though. That honor goes to the Mississippi River, which drains from 31 states—including Maryland—as well as two Canadian provinces.

"The continental divide runs through the middle of Maryland's westernmost county, Garrett County, and the highest mountain in the state, Backbone Mountain, is located there," said National Aquarium General Curator Jack Cover. "Rain falling on the western slopes of Backbone Mountain drains into the Mississippi watershed, while rain falling on the eastern slopes of Backbone Mountain drains into the Chesapeake Bay watershed."

The Mississippi River watershed is the fifth largest in the world, dwarfed by the Amazon River in South America, which drains from an area that stretches over 3 million square miles.

The fact is, no matter where you live, you live in a watershed—and probably more than one. Watersheds vary widely in size; smaller watersheds and subwatersheds are contained within larger ones.

A watershed is an area of land where rainwater, snowmelt and other forms of precipitation collect and drain into rivers, streams, wetlands, lakes and other bodies of water. This collection and drainage can happen in a few different ways. Precipitation can fall directly into these bodies of water. It can also enter them as runoff, landing on the ground and draining off from there (particularly impervious surfaces like roads or sidewalks). Or it can seep into the soil and then be slowly released. Once in a waterway, water flows from higher elevations into larger waterways at lower elevations, pulled by gravity.

In most watersheds, precipitation drains into a river basin and, ultimately, the ocean. In some inland watersheds, the water never reaches a river basin or the ocean, instead flowing into lakes and ponds.

A Map Showing the Four Subwatersheds—Gwynns Falls, Jones Falls, Back River, and Baltimore Harbor—Located within Baltimore City, Maryland.

Baltimore City is situated within the Patapsco and Back River Basin, which has four smaller subwatersheds within it—Baltimore Harbor to the south, in the heart of downtown; Gwynns Falls to the northwest; Jones Falls in the central north; and Back River to the northeast.

According to Blue Water Baltimore, a nonprofit that monitors and protects Baltimore's waterways, the city's four subwatersheds encompass a combined 194 square miles of land, 454 miles of waterways, and more than a million residents.

In this new story series, we're going to explore each of these four subwatersheds, and the waterways and neighborhoods within them. We hope you'll join us!

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