The viaduct, between Morfa Mawddach and Barmouth stations in Gwynedd, is used by rail, cyclists, motorcyclists and pedestrians and is part of the National Cycle Route 8.

The northern end of the viaduct, where the swing bridge is located, is next to Figle Fawr, a rock at the base of the Rhinogydd mountains.

[8] The nearest road across the Afon Mawddach is the toll bridge at Penmaenpool about 5 miles (8 km) upstream, which can carry vehicles up to 2.5 tonnes (5,500 lb).

[2] The footbridge is owned by Network Rail, and Gwynedd Council contributes 10 per cent of its annual maintenance cost in exchange for a licence to use it.

[11] A bridge across the Mawddach Estuary at Barmouth was proposed by the Aberystwith and Welsh Coast Railway, which constructed a line between Aberystwyth and Pwllheli.

Conybeare decided on the use of a timber viaduct because it was about four times cheaper to import wood from the Baltic by sea than to construct an iron bridge.

Early on, progress was hindered by strong tidal currents which caused multiple failed attempts to sink the bridge's piers from barges.

[4] Between March and June 1866, staging was built from the northern abutment for the bridge, and the piers were dropped into the water, bedded into the rock, and filled with concrete.

The water around the trestles had a maximum depth of 54 feet (16 m) at spring tides but the river bed was raised by tipping stones to protect the piles.

[4] In August 1899, Alfred Jones Collin, the chief engineer of Cambrian Railways (which had absorbed the A&WCR in 1865), ordered underwater inspections to check the integrity of the drawbridge span's ironwork.

[15] By 1980, the bridge's 500 timber trestle piles were under attack from marine woodworm at river bed level and the resulting damage was serious enough to threaten its closure.

[4] On 13 April 1986, a British Rail Class 37 diesel locomotive number 37427 was named Bont Y Bermo (Welsh for Barmouth Bridge) to celebrate the reintroduction of locomotive-hauled trains following repairs.

[21] In March 2013, the Barmouth Viaduct Access Group (B-VAG), was established to investigate an alternative route from the town centre to the bridge, as the walkway is steep, narrow, and unsuitable for pushchairs or wheelchairs.

[23] This is problematic as revenue from tolls is insufficient to cover the council's share of costs, and there is no budget to employ staff to collect payments.

[11] Gwynedd Council proposed closing the bridge to pedestrians and cyclists for cost reasons, as it needed to find £9 million of savings by April 2016.

A petition calling on the council to "cease considerations of closing this much loved walking and cycling route" attracted 20,000 signatures in a week.

[29] The same month, Bill Kelly, the chief operating officer of Network Rail Wales, spoke of unapproved ambitions to spend around £20 million to secure the long-term future of Barmouth Bridge between 2019 and 2024.

FSC-certified greenheart hardwood was sourced by NR from Guyana for its long track record of use in challenging applications, and preservative treatment is unnessary as it is resistant to attack by shipworm and wood rotting fungi.

[35] The work was completed and the track reopened after a three-month closure on 2 December 2023, with a formal opening ceremony on the following Friday attended by Wales Office minister Fay Jones, Senedd member Joyce Watson, the mayor of Barmouth and representatives of Network Rail and their engineering contractors.