JimDixon: Pick a spot on the ground. Imagine that a raindrop falls on that spot. Imagine that it doesn’t soak in, but it runs downhill. Which way will it go? Trace its path. Eventually, it will flow into a stream. That stream will flow into a bigger stream, which will flow into a river, which may flow into a bigger river, and so on, which will eventually reach the sea. The last river will have a name; let’s say it’s the Mississippi. That means your original spot was part of the Mississippi watershed. Sometimes large watersheds are divided into smaller watersheds named after the various rivers that flow into it; for example, the Mississippi watershed may be divided into the Ohio watershed, the Missouri watershed, and so on.
malwayslooking: ‘Watershed’ just indicates where all the water flows.
So a river, in the Chesapeake Bay watershed, will drain (or empty) into Chesapeake Bay. Or at least, into another river or lake system that eventually empties into Chesapeake Bay.