A large part of the valley of the Tamar is protected as the Tamar Valley National Landscape (an Area of Outstanding Natural Beauty), and some is included in the Cornwall and West Devon Mining Landscape (a World Heritage Site) due to its historic mining activities.

[8] The seventh-century Ravenna Cosmography mentions a Roman settlement named Tamaris, but it is unclear to which of those towns along the Tamar this refers.

[11][12] In November 2013, South West Water was fined £50,000 after it admitted permitting the discharge of sewage from its Camels Head treatment plant into a tributary of the River Tamar for eight years.

Rocky reefs in low salinity estuarine conditions far inland on the Tamar are very unusual and support species such as the hydroid Cordylophora caspia.

The site was designated in 1991 for its biodiversity and varying habitats that support a large number of wader and wildfowl species, as well as the special interest of its marine biology.

Remains include wheal or engine houses, deep and open cast mines dating from the Bronze Age through to the medieval and modern era, the export docks at Morwellham Quay were once an international centre of trade in copper, lead and arsenic.

[19] According to Ordnance Survey mapping, the source of the Tamar is at Woolley Moor, approximately 3.5 miles (5.6 km) from the north Cornish coast, at 50°55′06″N 4°27′48″W / 50.9184°N 4.4633°W / 50.9184; -4.4633.

[27] The location of the spring is a "high windswept plateau largely devoid of farmland, and inhabited by stunted trees and wiry undergrowth.

The county boundary was restored to the Tamar in 1966, when the civil parishes of North Petherwin and Werrington were transferred from Devon to Cornwall.

This "centre of river" arrangement ends just upstream of the Tamar Bridge at Saltash, downstream of which the counties officially extend only to their respective (tidal) bank's low water mark.

The Calstock Viaduct is another notable structure on the Tamar, being 120 feet (37 m) high with twelve 60-foot (18 m) wide arches, of which three of the piers stand in the river, and was built between 1904 and 1907.

[33] The normal tidal limit (noted on Ordnance Survey maps as 'NTL') is a weir just downstream of the village of Gunnislake.

Waterborne traffic through the Hamoaze is controlled by the Queen's Harbour Master for Plymouth,[34] who is responsible for managing navigation along the entire tidal Tamar.

[35] The Royal Navy has one of its three main naval bases at Devonport, situated on the Hamoaze, upstream of which the river is now used largely by recreational craft.

[37] A typical Tamar vessel was a sailing barge, built on the open river bank, of up to 60 tons, with a peaked, gaff-rigged mainsail and a fore staysail.

[38] The Tamar was navigable by seagoing ships of up to 400 register tons as far inland as Weir Quay,[39][40] near Bere Alston, where the estuary narrows into the tidal river, some 8.4 miles (13.5 km) upstream from Plymouth Sound.

[33] The import of fertilizer (at the time of the construction of the canal all types of which were typically referred to as "manure") and coal and the export of bricks and granite along this short navigation proved profitable for many years.

[47] In 997 according to the Anglo-Saxon Chronicle, raiding Vikings travelled up the Tamar and then the Tavy river as far as Lydford, and burned Ordwulf's monastery at Tavistock.

[50] In medieval times the transport of goods to supply the Benedictine abbey at Tavistock, four miles by track from the river port of Morwellham, was significant.

[51] Sea sand from the coast was imported to spread on farmland, until in the 18th century a dressing of lime was found to be more beneficial.

[53] Other significant cargoes exported were quarried granite, and later, copper, lead and manganese ores, with their important by-product of arsenic.

The development of the "Three Towns" (Plymouth, Devonport and Stonehouse) at the mouth of the river offered an important market for the valley's agricultural produce, needed in particular to serve the victualling requirements of the royal dockyard, and this was always carried by boat.

[58] The growing city population created a large demand for sightseeing cruises on the river; this was a significant source of traffic from 1823, with the launch of the Cornish steam packet Sir Francis Drake, until the outbreak of World War II.

Tourist and market traffic on the river, using purpose-built or converted steamers, remained substantial until the Devonport piers were closed and the ships requisitioned on the outbreak of war in 1939.

[59] Rocks around the edge of Dartmoor were mineralised by fluids driven by the heat of the Earth's core, which gave rise to ores containing tin, copper, tungsten, lead and other minerals in the Valley.

[64] A traditional Cornish tale claims that the devil would never dare to cross the River Tamar into Cornwall for fear of ending up as a pasty filling.

He became even more enraged and cast a spell on Tamara, turning her into a bubbling spring, which produced the Tamar river and flowed all the way to the sea.

Tawradge was never able to find and merge with his beloved Tamara, instead turning north toward Bideford and the Bristol Channel and is still said to mourn his love, the Tamar.