The River Coquet /ˈkoʊkət/ runs through the county of Northumberland, England, discharging into the North Sea on the east coast at Amble.

The upper reaches are bordered by the Otterburn Ranges military training ground, and are crossed by a number of bridges built in the 20th century.

It passes a number of small villages and hamlets, and feeds one of the lakes created by extraction of gravel that form the Caistron Nature Reserve, before reaching the town of Rothbury, where it is crossed by a grade II listed bridge.

One of the earliest was on Hepden Burn, a tributary in the upper reaches, which was mentioned in the early 13th century, but was not subsequently developed, due to unrest in the area.

Archaeological investigation between 2010 and 2013 revealed one of the few unaltered medieval mill sites in Britain, and pushed the development of the breast-shot water wheel back by three centuries.

The river, which is about 56 miles (90 km) in length,[1] rises in the Cheviot Hills close to the 1,440-foot (440 m) contour, to the east of Grindstone Law and to the north of Ravens Knowe.

The border between England and Scotland follows it briefly, before turning northwards at Chew Green, where there are the remains of Roman camps on the north bank of the river, the course of Dere Street, locally named as Camelspath, crosses the river, and there are the remains of the medieval village of Kemylpethe.

The village has a Holy Well, with a rectangular stone tank dating from Roman times, but the fact that Bishop Paulinus baptized around 3000 Northumbrians there in the year 627 is now thought to be based on a misreading of the writings of Bede.

The well is a grade I listed structure, and there is a Roman road which passed through the well enclosure and then crossed the Coquet on its way from High Rochester fort to the River Aln.

By the time the river reaches Hepple bridge, which consists of modern steel beams resting on piers dating from around 1874,[12] it has dropped below the 330-foot (100 m) contour.

It turns to the north-east, and then passes the hamlet of Caistron, where there are two large lakes[3] caused by extraction of sand and gravel, which started in 1956.

Traffic from the quarry crossed a curious bridge, which consists of large metal tubes laid onto the bed of the river, above which the roadway has been constructed.

[14][3] The river continues to the south of Thropton where Wreigh Burn joins from the north, and passes through Rothbury, where a bridge dating from the 16th century crosses it.

Built as a packhorse bridge, it was made wider in 1759 by William Oliphant, a mason from Rothbury, to accommodate vehicles, and was further widened in the 20th century, when the parapets were removed and a concrete deck constructed on top of the original structure.

[20] It then loops around a finger of land, which was given by its owner, William Bertram lord of Mitford, to Augustinian canons between 1130 and 1135, who founded Brinkburn Priory.

[24] After passing through Weldon, where there is a mill and a three-arched bridge dating from 1760, which is thought to have been designed by the engineer John Smeaton,[25] the Coquet is crossed by the A1 road.

It was designed to discharge 19,000 cubic feet (539 m3) of treated effluent to the river each day, and replaced old inefficient works at Felton, Longframlington, Swarland and Thirston.

[32] At the eastern end of the site is Factory Bridge, consisting of three segmental arches, which was built of rock-faced stone in 1865.

[35] The East Coast Main Line crosses the river on a railway viaduct with nine arches, designed in Robert Stephenson and completed in 1849 or 1850.

The fish pass was refurbished in 2013 after lying derelict for 20 years, to prevent harm to salmon, sea trout and eels, which were being injured while trying to negotiate the main weir.

It was abandoned by 1567, but remains one of the best preserved and elaborate monuments of its type in the British Isles, and is a grade I listed structure.

[39] On the tidal section, a loop to the north encloses the centre of Warkworth, including its medieval castle and church.

[42] This process, which removed grease and other impurities from the woollen fabric and knitted the fibres together to form a denser product, was a manual one until the 12th century, with the cloth put into tubs and trampled by foot, before it was washed in a stream.

The fulling mill used a rotating shaft with cams to raise and drop mallets onto the cloth, which was immersed in tubs.

[47] Smeaton's dam at Guyzance fed the iron and tin works, which was later converted to a woollen mill, producing blankets.

Warkworth Mill was one of the earliest on the river,[47] as the rent from it was used to provide a light in St Cuthbert's shrine in 1214, and this was still the arrangement in 1400.

[55] This can be roughly translated to 'Red River', perhaps reflecting the red porphyritic pebbles found here in large numbers.

[citation needed] The Environment Agency measure the water quality of the river systems in England.

The reasons for the tidal section being less than good are physical modification of the channel and run-off of nutrients from agricultural land.

Like most rivers in the UK, the chemical status changed from good to fail in 2019, due to the presence of polybrominated diphenyl ethers (PBDE), perfluorooctane sulphonate (PFOS) and mercury compounds, none of which had previously been included in the assessment.