The River Plym is a river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 in Devon

Devon

Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...

, England. Its source is some 450m (about 1500 ft) above sea level

Sea level

Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

 on Dartmoor

Dartmoor

Dartmoor is an area of moorland in south Devon, England. Protected by National Park status, it covers .The granite upland dates from the Carboniferous period of geological history. The moorland is capped with many exposed granite hilltops known as tors, providing habitats for Dartmoor wildlife. The...

, in an upland marshy area called Plym Head. From the upper reaches

Upper Plym Valley

The Upper Plym Valley is an area of Dartmoor, Devon, England, particularly noted for a large array of archaeological sites rnging from prehistoric Drizzlecombe to 19th century Eylesbarrow Mine...

 which contain antiquities

Antiquities

Antiquities, nearly always used in the plural in this sense, is a term for objects from Antiquity, especially the civilizations of the Mediterranean: the Classical antiquity of Greece and Rome, Ancient Egypt and the other Ancient Near Eastern cultures...

 and mining

Mining

Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...

 remains the river flows roughly southwest and enters the sea near (and gives its name) to the city of Plymouth

Plymouth

Plymouth is a city and unitary authority area on the coast of Devon, England, about south-west of London. It is built between the mouths of the rivers Plym to the east and Tamar to the west, where they join Plymouth Sound...

, where the settlement was historically known as Sutton. Its tidal estuary is known as the Laira

Laira

Originally Laira was the name given to that part of the Plym estuary from the Cattewater up to Marsh Mills, Plymouth. It is also a name used to refer to the area of Plymouth situated around the Laira Traction Maintenance Depot. Much of the housing in the area was build around 1900 for employees of...

. It is approximately 30 km (about 20 mi) long.

The name Plym is thought to have its origins in Old English and means the 'plum tree', from a back-formation from the name of Plympton

Plympton

Plympton, or Plympton Maurice or Plympton St Maurice or Plympton St Mary or Plympton Erle, in south-western Devon, England is an ancient stannary town: an important trading centre in the past for locally mined tin, and a former seaport...

.

, a River-class antisubmarine frigate

River class frigate

The River class frigate was a class of 151 frigates launched between 1941 and 1944 for use as anti-submarine convoy escorts in the North Atlantic....

, was named after the river during World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

. It carried out convoy

Convoy

A convoy is a group of vehicles, typically motor vehicles or ships, traveling together for mutual support and protection. Often, a convoy is organized with armed defensive support, though it may also be used in a non-military sense, for example when driving through remote areas.-Age of Sail:Naval...

 escort duties in the North Atlantic

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

 and was later destroyed in the UK's first nuclear explosion.

When it was in operation, the Cann Quarry Canal

Cann Quarry Canal

The Cann Quarry canal was a canal in Devon, England which ran for just under from Cann Quarry to the River Plym at Marsh Mills . The canal was first proposed in 1778 but then largely remained in stasis until 1825. The canal was opened as a tub-boat canal on 20 November 1829...

 left the river at Marsh Mills.

The Plym Valley Railway

Plym Valley Railway

The Plym Valley Railway is part of the closed South Devon and Tavistock Railway near Plymouth, a branch line of the Great Western Railway in Devon.The Plym Valley Railway is currently rebuilding the Marsh Mills to Plym Bridge section of the line...

is a volunteer run railway which operates steam and diesel hauled train rides along a section of the Plym Valley from Marsh Mills station. The railway is currently extending its line to Plymbridge.