The St. Martin River is a tributary of Isle of Wight Bay

Isle of Wight Bay

Isle of Wight Bay is a lagoon that separates part of mainland Worcester County, Maryland from the southern part of Ocean City, also in Worcester County. It is crossed by the U.S. Route 50 bridge into Ocean City as well the Maryland Route 90 bridge. The major tributary of Isle of Wight Bay is the...

 in Worcester County, Maryland

Worcester County, Maryland

-2010:Whereas according to the 2010 U.S. Census Bureau:*82.0% White*13.6% Black*0.3% Native American*1.1% Asian*0.0% Native Hawaiian or Pacific Islander*1.7% Two or more races*1.3% Other races*3.2% Hispanic or Latino -2000:...

. Approximately 4.4 miles (7.1 km) long, it drains the northernmost part of Worcester County.

A short river, the St. Martin broadens rapidly to enter Isle of Wight Bay

Isle of Wight Bay

Isle of Wight Bay is a lagoon that separates part of mainland Worcester County, Maryland from the southern part of Ocean City, also in Worcester County. It is crossed by the U.S. Route 50 bridge into Ocean City as well the Maryland Route 90 bridge. The major tributary of Isle of Wight Bay is the...

 where the bay is crossed by Maryland Route 90

Maryland Route 90

Maryland Route 90 is a state highway in the U.S. state of Maryland. Known as the Ocean City Expressway, the state highway runs from U.S. Route 50 near Whaleyville to MD 528 in Ocean City. MD 90 is a two-lane expressway that provides one of the main access routes to Ocean City, especially the...

. Most of the river is a tidal 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....

. Its two main tributaries are the Bishopville Prong and the Shingle Landing Prong.

The St. Martin forms the northern boundary of Ocean Pines, Maryland

Ocean Pines, Maryland

Ocean Pines is a census-designated place in Worcester County, Maryland, United States. The population was 11,710 at the 2010 census. It is the principal of and is included in the Ocean Pines, Maryland Micropolitan Statistical Area, which is included in the Salisbury-Ocean Pines, Maryland Combined...

; Bishopville, Maryland

Bishopville, Maryland

Bishopville is a small unincorporated community 10 miles north of Berlin in Worcester County, Maryland, located at . The community is just south of the Delaware state line....

is on the Bishopville Prong of the river.