The Magothy is a relatively small, mostly tidal river with a watershed area (including the water surface) of 44 square miles (110 km²), or 35 square miles (91 km²) of land. Thus, its total watershed area is 20% water. It starts in Anne Arundel County in Severna Park, and flows into Chesapeake Bay next to Gibson Island. It is probably best known among recreational boaters for the popular anchorage behind Dobbins Island. Its navigable tidal portion is crossed by one bridge, located on Magothy Bridge Road in Pasadena. Its upper, nontidal portion is called Magothy Branch, and is dammed at MD 648 (Baltimore-Annapolis Boulevard) to form Lake Waterford (there was an old mill dam at the same site). Some of the creeks on its south shore drain highly developed portions of Severna Park and Arnold, especially North Cypress Creek, which drains much of the Park Plaza and Giant shopping centers along Ritchie Highway north of McKinsey Road.

The Baltimore Light Station marks the mouth of the river.

Almost all of the creeks and tidal coves on the Magothy are named, as the result of a project started in 2001 by the Magothy River Association, and funded by the Chesapeake Bay Trust. They are shown on this map produced as part of that project,^[6] and the major ones are shown on this topographic map.^[7]

There are nine creeks along the Upper Magothy River. None of them are navigable so none are shown on any published maps, except the map produced by the Magothy River Association. All have historical names except where noted.

Magothy Branch (nontidal upper Magothy, drains to Lake Waterford)

North shore, upriver to downriver:

Muddy Run

Bailys Branch

Brookfield Branch (nearest community)

Beachwood Branch (nearest community)

Indian Village Branch (nearest community; mouth hard to see)

South shore, upriver to downriver:

Kinder Branch (starts in Kinder Park, drains to Lake Waterford)

Rouses Branch (also starts in Kinder Park and drains to Lake Waterford)

Nannys Creek (mouth hard to see)

From Cockey and Old Man creeks downriver, most of the creeks and coves are navigable. Thus, most of them have names on published maps, since they have been named for longer.

On the north shore, from upriver to downriver, the navigable, named creeks and tidal ponds are:

Cockey Creek

Ross Cove

Blackhole Creek

Broad Creek

Park Lake

Park Creek

Dobbins Pond

Long Cove

Grays Creek (with north & south branches)

Cornfield Creek

James Pond

Redhouse Cove

On the south shore, from upriver to downriver, the navigable, named creeks and tidal ponds are:

Old Man Creek

Tar Hill Cove

Cattail Creek (includes Cold Spring Cove)

Cypress Creek (including North Cypress Creek and Browns Cove)

Dividing Creek (includes Buckinghams Cove)

Mill Creek

Spriggs Pond

Bohdal Pond

Forked Creek (includes Cool Spring Cove)

Scheides Cove

Lake Placid

Deep Creek

Little Magothy River