What is a watershed anyway? – understanding the Chesapeake Bay watershed

A lot of us clean water enthusiasts have probably heard the word “watershed” countless times, but what does the word actually mean? Even though I’m a conservation professional, it took me longer than I’d like to admit to understand the complexity of the concept, just as it took a while to learn the seemingly endless acronyms like HUC (hydrologic unit code) and TMDL (total maximum daily load) — but acronyms are a conversation for another day. For now, let’s explore what makes a watershed, and why the Chesapeake Bay watershed is so important!

An unnamed tributary of the east branch of Codorus Creek near Winterstown in York County, PA.

What is a watershed?

At its most basic level (no pH pun intended), a watershed is an area of land where all water, whether from rain, snowmelt, springs or streams, flows toward a common body of water, such as a river, lake, or even an ocean.

Some watersheds can be very small, draining into a quaint nearby lake, while others, like the Chesapeake Bay watershed, can encompass thousands of square miles and include an endless variety of sources like streams, rivers, lakes, reservoirs and more. In any given watershed, water from up to thousands of sources can flow from higher ground smaller waterbodies to progressively larger ones, all ending up at its final destination – the large waterbody.

Watersheds are ultimately determined by topography and gravity — with all water flowing to the lowest point it can find. That water in your local park or flowing down the street after a storm is all heading to the same place. That’s why our collective efforts to manage water and reduce pollution are so important.

A bird’s eye view of the Codorus Creek tributary in York County, PA.

The Chesapeake Bay watershed

Home to over 18 million people and more than 3,000 plant and animal species, the Chesapeake Bay watershed spans 64,000 square miles, stretching across New York, Pennsylvania, Delaware, Maryland, Virginia, West Virginia, and Washington, D.C. To put that into perspective, that’s more than 14 times the size of the Chesapeake Bay itself! It’s amazing that water from New York can find its way all the way down to the Bay.

The Chesapeake can’t boast the “largest watershed” award — that honor goes to the Mississippi River watershed — but the Bay does have the largest land-to-water ratio in the world: 14 square miles of land for every square mile of water! That’s more land than anywhere else that we have the responsibility of protecting.

All that land in the watershed allows big species with large ranges, like this elk, to thrive.

If you’ve heard of the Susquehanna, Potomac, James, York or Choptank rivers, chances are you live in the Chesapeake Bay watershed and are supplied with fresh water by one of those main sources. However, more than 150 major rivers and streams flow into the Chesapeake Bay, with the Susquehanna River contributing nearly half of the Bay’s freshwater supply.

Unfortunately though, as water travels, it can pick up pollutants, moving down the line and ultimately into the Bay — something to consider seriously, as the rivers and streams in the watershed provide not only habitat for all aquatic life but also drinking water to millions of people. The health of the Bay is closely linked to land use practices within the watershed. Pollution from our homes, cars, cities, farms and industries all directly impact water quality.

The Chesapeake Bay is also one of the most biologically rich estuaries in the world. Wetlands, forests, and underwater grasses provide critical habitat for wildlife and help maintain clean water. Those are free benefits worth conserving! On top of that, the Bay is central to the region’s economy, supporting industries like commercial fishing, tourism, and agriculture. We all love the staple blue crabs and oysters, with maybe a little too much Old Bay. Not only are these industries economically important, they’re extremely culturally important to Bay residents.

The good news is there are plenty of actions we can talk to help ensure cleaner water for all 18 million of us.

Freshly-caught blue crabs, one of the many iconic and deeply culturally significant species of the Chesapeake Bay

Make your own Impact

Luckily, there are plenty of farmers employing conservation practices, homeowners introducing stormwater management installations, and local governments and municipalities asking the right questions to move forward sustainably.

These efforts are reducing nutrient pollution that would otherwise end up in the Bay. Excess nitrogen and phosphorus from fertilizers, sewage, and stormwater runoff lead to algae blooms, which create dead zones (low-oxygen areas harmful to fish and marine life). Urban development and deforestation are also reducing natural water filtration, leading to erosion and pollution.

Large-scale issues like these can seem daunting. I feel powerless sometimes, but I remember our small, collective actions can always contribute to the health of the watershed. Try something as simple as reducing the amount of fertilizer you use to minimize nutrient runoff, or being scrupulous about picking up pet waste, to keep both nutrients and bacteria out of the waterways. You might also volunteer for streamside trash cleanups or tree plantings in your community.

The Chesapeake Bay watershed is a vital natural resource that provides clean water, supports biodiversity, and sustains local economies. Let’s all come together and do what we can to ensure clean water for us, the flora, and the fauna that makes this one of the most special, beautiful, and beneficial regions to call home.

If you love the land, water, and wildlife of the Bay as much as we do, explore our volunteer opportunities or support the Alliance’s clean water efforts!