Middle River is an estuary

Estuary

An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....

 in Baltimore County

Baltimore County, Maryland

Baltimore County is a county located in the northern part of the US state of Maryland. In 2010, its population was 805,029. It is part of the Baltimore-Washington Metropolitan Area. Its county seat is Towson. The name of the county was derived from the barony of the Proprietor of the Maryland...

, Maryland

Maryland

Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...

, located about 5 miles (8 km) east of the city of Baltimore. The estuary extends from the community of Middle River

Middle River, Maryland

Middle River is an unincorporated community and a census-designated place in Baltimore County, Maryland, United States. The population was 23,958 at the 2000 census...

, north of the Martin Plaza Shopping Center, to the southeast for about 4 miles (6.4 km), to the Chesapeake Bay

Chesapeake Bay

The Chesapeake Bay is the largest estuary in the United States. It lies off the Atlantic Ocean, surrounded by Maryland and Virginia. The Chesapeake Bay's drainage basin covers in the District of Columbia and parts of six states: New York, Pennsylvania, Delaware, Maryland, Virginia, and West...

. The watershed

Drainage basin

A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

 area of Middle River is 12 square miles (31 km²), and includes Martin State Airport

Martin State Airport

Martin State Airport is a public use airport located nine nautical miles east of the central business district of Baltimore, in Baltimore County, Maryland, United States...

.

Tributaries of Middle River

Clockwise from the southern edge of its mouth, they are:

• Sue Creek
• Hogpen Creek
• Norman Creek
• Hopkins Creek
• Upper Middle River (no separate name)
• Dark Head Creek; its nontidal portion is Cowpens Run; Martins Lagoon is the upper tidal portion near Martin State Airport (neither of the latter two names are official feature names in GNIS)
• Stansbury Creek
• Frog Mortar Creek
  Frog Mortar Creek
  Frog Mortar Creek is a tidal creek in Baltimore County, Maryland. The creek empties into the Middle River and surrounds the northeast and southeast sides of Martin State Airport.-External links:*...
  
  
• Galloway Creek