A £9 million project led by Natural Resources Wales is restoring four of the country’s most important rivers. On the Tywi, weirs, culverts and bridge aprons that blocked fish for decades are being opened up, and the first monitoring results are encouraging.
The River Tywi is about 120 kilometres long, one of the longest rivers that flows entirely within Wales. It rises at just over 430 metres in the Cambrian Mountains and runs through steep gorges and pool and cascade sequences before meandering across a broad floodplain to Carmarthen Bay. It is home to Atlantic salmon, sea trout, eel, three species of lamprey, twaite and allis shad and bullhead.
It was once a remarkably productive fishery. At its peak, from the 1970s to the early 1980s, average annual catches exceeded 2,000 salmon and 10,000 sea trout. Today, catches of both are below 10 per cent of those levels and the populations are considered at risk. Eel numbers are thought to have fallen by about 90 per cent, and all of the lamprey species are classed as threatened or near threatened.
A project for four rivers
The Tywi is one of four rivers at the heart of Four Rivers for LIFE, alongside the Teifi, Cleddau and Usk. All four are Special Areas of Conservation, and all four are in unfavourable condition. The project is led by Natural Resources Wales and funded through £9 million from an EU LIFE programme grant, with support from the Welsh Government and Dŵr Cymru Welsh Water.
Its partners include the Bannau Brycheiniog National Park Authority, the River Restoration Centre, the Agricultural Research Centre at Coleg Sir Gâr, and the Woodland Trust, with West Wales Rivers Trust helping on the ground. Together they aim to improve 776 kilometres of river in mid and south Wales. The targets include improving fish passage at 12 sites, planting 50,000 native trees and working with 350 farms to reduce the nutrients and sediment reaching the water.
Opening the Tywi
Barriers to fish migration have been a major focus on this river. By the end of 2025, Natural Resources Wales had addressed seven barriers in the Tywi catchment, opening up about 40 kilometres of river.
At Jerusalem weir, on the Afon Clydach near Llangadog, a 2.5 metre high weir was fitted with a Larinier fish pass in summer 2024, with a bristle side slot to help eels climb past. In October 2024, work at the railway crossing on the Afon Dulais at Llanwrda added pre barrages and a studded tile ramp across a 14 metre bridge apron. In summer 2025 a rock ramp with four pre barrages was built over 50 metres at the Llanwrda road bridge, again with a studded tile ramp for eel and lamprey.
Combined with a fish pass completed at Llanwrda village weir in 2023 by the Natural Resources Wales Salmon for Tomorrow project, those schemes have opened more than 12 kilometres of habitat on the Dulais.
In October 2025, on the Afon Lwynor, a tributary of the Bran near Llandovery, a culvert two metres in diameter and 12 metres long was replaced with a clear span bridge, restoring access to 4.5 kilometres of upstream habitat.
Working with farmers
Much of the Tywi runs through farmland, and the project has worked closely with landowners. Some 14 kilometres of fencing has been completed on the Tywi to keep livestock off the riverbanks, with drinking troughs installed where needed, for example at Dyffryn Isaf Farm on the Cothi.
The project is also tackling invasive plants. A giant hogweed infestation near Manordeilo has been treated over several years and the species is now close to being eliminated from the catchment. Himalayan balsam is being controlled on the Bran and Marlais, with contractors and volunteers from West Wales Rivers Trust, and a rust fungus is being trialled as a natural biocontrol.
Early results
Across all four rivers, Natural Resources Wales reported in September 2025 that around 37,000 native trees had been planted, 40 kilometres of fencing installed, more than 5,000 metres of invasive species removed and eight fish barriers improved, with seven more to follow in 2025 and 2026.
Monitoring is now showing what that work means for fish. On the Tywi, early electric fishing results show more salmon fry on the Clydach at most sites upstream of Jerusalem weir. On the Cleddau, where boulders were returned to reaches from which they had been dredged, brown trout numbers increased substantially, with smaller gains for salmon and bullhead. On the River Senni, a tributary of the Usk, a large increase in juvenile salmon was recorded upstream of a pipe bridge that was replaced with a clear span bridge by Powys County Council with project support.
Writing about the first year of results, Sophie Gott, the project’s Monitoring Officer, said: “we are cautiously optimistic that these data show our river restoration work is doing what it was intended to do.”
What comes next
Major pieces of work lie ahead on the Tywi. With the National Trust, the project has been preparing the Dinefwr Floodplain Restoration Project, which aims to restore oxbow lakes, pools, wetland vegetation and floodplain grassland within the Dinefwr Floodplain National Nature Reserve. And the project announced plans for a trial release of 200 juvenile freshwater pearl mussels, a critically endangered species, at three sites including one in the Tywi catchment.
The success of the LIFE projects has also shaped what Natural Resources Wales does next. Nick Thomas, its Strategic Projects Manager, said: “Encouraged by the progress of the LIFE projects, in 2024, NRW launched the Upper Wye Project.”
For fisheries professionals, Four Rivers for LIFE is a clear demonstration of how barrier removal, farm partnerships, habitat restoration and monitoring can work together at catchment scale. The Tywi will take years to recover the runs it once supported, but the fish now have tens of kilometres of river that were closed to them a few years ago, and more young salmon are already showing up above barriers that once held them back.