A primer on the basics of the Chesapeake Bay

If you walk onto the Mayo Bridge by Shockoe Slip and drop a line on the downstream side, you essentially are fishing in the Chesapeake Bay.

If you dump pollution in the Shenandoah River, beyond the Blue Ridge Mountains, you can hurt the bay.

As we try to restore the Chesapeake, it helps to ask: Where is the bay, and what are we trying to restore?

Your basic bay

Experts call the 200-mile-long expanse of water from Norfolk to Havre de Grace, Md., the "main stem" of the bay. At its widest point, near the mouth of the Potomac River, it is about 35 miles across.

That probably is what most people consider the bay.

The big bucket

The Chesapeake Bay is an estuary, an area where fresh water flowing from land meets salt water from the sea.

The Chesapeake Bay, as a natural system, includes the tidal portions of the rivers that flow into it, experts say.

And that includes the James River up to the fall line -- the place where, if you moved up the river with the tide, you hit the first rapids.

The Mayo Bridge -- also called the 14th Street Bridge -- divides those two zones, with roaring rapids on the west side and tidal waters to the east.

"The Chesapeake Bay starts under 14th Street Bridge," said Greg Garman, a Virginia Commonwealth University fisheries ecologist. "There's probably a little artistic license, but fundamentally I don't see anything wrong with saying that."

Even though the James doesn't get salty until just below Hopewell, classic bay species such as blue crabs, mullet, flounder and young menhaden, spot and croaker frequent the James all the way up to downtown Richmond, Garman said.

Mike Gerel, a scientist for the Chesapeake Bay Foundation, an environmental group, sees the bay and its tidal tributaries -- not only the James, but also the Rappahannock River, the Potomac and others -- as a bucket. That's the place where the pollution goes.

Streams that feed these tidal areas are like little hoses filling the bucket, Gerel said. "What we're hoping to restore is the bucket."

The true footprint

Cleanup officials are working throughout the bay's watershed. That's the area in which all flowing waters -- including Gerel's hoses -- move toward the bay, picking up pollutants along the way.

That watershed covers more than 64,000 square miles in parts of six states -- Virginia, Maryland, Delaware, New York, Pennsylvania and West Virginia -- and the District of Columbia.

More than half of Virginia, from the Tri-Cities area north, lies in the bay watershed.

Cleaning streams in the watershed will affect people far from the coast.

"Even if you don't care about the bay," Gerel said, "you care about the stream in your backyard."