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​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​The Taff​ Fechan

The Taff Fechan rises immediately to the south of Pen y Fan and runs through the two Neuadd reservoirs then Pentwyn/Dolygaer, and finally Pontsticill Reservoir. 

The river emerges from the Pontsticill reservoir in the form of compensation water decided by Act of Par​liament when the reservoir was being built. The flow was in excess of 6.2 million gallons until 1955 when Parliament gave the Taf Fechan Water Board permission to reduce the flow to 4.2 million gallons per day, provided it was in a continuous and regular flow.  The local fishing club has fought hard to keep this flow as successive bodies have tried by various means to reduce it without recourse to Parliament.​​

 Ponsticill Reservoir

​​The river’s journey continues over mainly limestone strata with a rapid drop into the Blue pool at Pontsarn. Just below this point the Nant Glais enters the river from a caving system, while the imposing Pontsarn Viaduct that carried the railway from the valleys to Brecon stands above. From here the Taf Fechan progresses through a deep wooded gorge with steep sides rising up to the Gurnos Estate on one side and the Trefechan Estate on the other, finally joining the Taf Fawr at Cefn Coed–Cymmer.

Upstream of the confluence with the Taff Fawr, water was taken out of the river through a leat to supply the Cyfarthfa Iron Works and the ornamental lake in the grounds of Cyfarthfa Park. The water flowed from the leat through a series of pipes and aquaducts to the iron works, including Pont-y-Cafnau bridge which still stands today. 

The river is an excellent brown trout river and above Pontsarn it is a dedicated wild brown trout fishery, only restocked with fry bred from natural river fish. The Trust is seeking to improve access for migratory fish to spawn.​

The Taf Fawr

The Taf Fawr rises below Corn Du, south-west of Pen y Fan and flows south under the A470 through Beacons, Cantref  and Llwyn-on reservoirs.

From Llwyn-on reservoir it runs through mainly farmland for three miles before entering a gorge just above Cefn Coed and flowing over mainly limestone strata before meeting with the Taf Fechan.  Just below the gorge is the Cefn Coed Viaduct, another master piece of engineering that spans the valley at the point where the Nant Ffrwd enters the Taf Fawr. This viaduct linked with the Pontsarn Viaduct.

The Taf Fawr was also used by the Cyfarthfa Iron Works as a source of water for their iron making process.  The water was again taken via a leat but part of this leat cuts through a mountain before it emerges from underground approximately 800 metres from the confluence of the two rivers.  Taking the water out of the two rivers some distance from the works gave the head required to feed into the site.​

The iron works closed in the 1920’s and the leats were then used to feed a power house producing electricity for the town of Merthyr Tydfil.  The discharge from the powerhouse then ran back into the river where, 300 metres down stream, it was retained behind a dam  beside which a turbine was installed, again to produce electricity.  Hydro power is not new!

The Taff from Merthyr to Cardiff

From the confluence of the Fechan and Fawr, the river flows through Merthyr Tydfil where the once heavily polluted Nant Morlais joins. Just downstream is a new fish pass installed by Environment Agency Wales to enable trout and salmon to pass the weir.  It is proving to be very successful. Downstream of Merthyr Tydfil but close to the town the Nant Rhydycar joins the Taff.

From here the Taff begins to wend its way through all the villages that have been built along its banks -   Pentrebach, Abercanaid,  Troedyrhiw,  Merthyr Vale and Aberfan towards Quakers Yard.   The Taff Bargoed  enters the river at the Quakers Yard gorge.  The gorge is a natural obstacle and is worth a visit during October or November to see the salmon negotiating it to get upstream.   Below this the Afon Cynon merges with the Taff and, slightly further downstream, the Nant Clydach joins it.  The Trust has carried out some work on the Clydach. (See Projects)

At Pontypridd the Taff is joined by the River Rhondda.  The Rhondda was once badly polluted by the numerous coal mines that were in the valley and is made up of the Rhondda Fawr and the Rhondda Fach, both now home to a good head of resident brown trout as well as the increasing runs of migratory salmon.  Just below Pontypridd is a major weir that was used to take water from the Taff.  This was a major obstacle to migratory fish and the point where the water was removed for industry has now been used to form a fish pass for salmon and trout as well as other fish.

 Cardiff Bay

The river runs on through Taffs Wells and Radyr and then into the confines of Cardiff Bay. The bay is a major attraction for Cardiff and has undoubtedly helped to make Cardiff more popular with tourists and visitors in general.  However, it has brought with it two unwanted visitors, namely the zebra mussel and a shrimp from the continent called dikerogammarus villosus. This shrimp can do untold damage to our native species.  There are strict bio-security measures in place around Cardiff bay to try to contain both these species and stop them from spreading else where.