Margaret Greenberg, age 14, of Pittsfield, Mass., for her question:

BOW LARGE IS CHESAPEAKE BAY?

Chesapeake Bay is actually a long arm of the Atlantic Ocean. It stretches about 200 miles northward through Virginia and Maryland. The bay varies in width from three to 25 miles. It is the largest bay along the East Coast of the United States.

At the northern end of Chesapeake bay is the submerged or drowned southern end of the Susquehanna River, which divides the state of Maryland into two parts.

Five important rivers empty into the bay on the west: the Patuxent, Potomac, Rappahannock, York and James. Three important rivers come into the bay from the east: the Pocomoke, Choptank and Nasticoke. Ail of these rivers as well as many smaller creeks have submerged mouths. This tends to give the bay an extremely irregular and long shore.

Chesapeake Bay's entrance is 13 miles wide and it is between Cape Henry and Cape Charles. Crossing it at this point is the Chesapeake Bay Bridge Tunnel, which was completed in 1964.

The two chief port cities on the bay are Baltimore, Md., and Norfolk, Va. The bay rarely freezes during the winter because it is far enough south.

The bay was named for the Chesapeake Indians, who called it the Great Salt Water. It is one of the earliest areas to he settled.

In 1814 the British fleet entered the bay and then sailed up the Potomac River to burn Washington. Earlier, the French fleet had sailed into the York River and helped to end the American Revolution at Yorktown. And on the bay at Hampton Roads, the Monitor and the Merrimac fought a famous Civil War battle.

Chesapeake Bay is part of the Intracoastal Waterway. It is linked with Delaware Bay by the Chesapeake and Delaware Canal and, at its southern end by similar canals to Albemarle Sound in North Carolina.

Chesapeake Bay has important military, economic and recreational values. Just up the Potomac River from Chesapeake lies the nation's capital, Washington, D.C. Also on the bay is Annapolis, Md., the location of the United States Naval Academy.

A great naval base is located at Hampton Roads, at the mouth of the James River.

Also enjoying the bay , especially during the summer months, are the owners of thousands of private pleasure boats.

The bay is the leading source of oysters and blue crabs in the United States. Menhaden, Potomac herring and other fish also are caught there.

Some parts of Chesapeake Bay are so shallow that channels must be dredged to enable large ships to reach their ports. Much of this work is done by the U.S. government.