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Llŷn has many small streams, but few rivers. The Welsh for river, Afon, is used much more widely than it's English equivalent, and many so called "Afon"s are really only streams (nant is stream in Welsh). This guide starts with the largest rivers.

On this page:

Afon Dwyfor
Afon Dwyfach
Afon Erch
Afon Soch
Afon Rhyd-hir
Afon Penrhos

Afon Dwyfor

Dwyfor: dwy - two; for from môr - sea. The district of Dwyfor, which covers the Llŷn Peninsula and a slice of western-central Snowdonia is named after this river. The Afon Dwyfor rises in the western mountains of Snowdonia and flows down through Cwm Pennant towards the lower land of the peninsula. Cwm Dwyfor, where the source of the river is, lies between Moel Hebog and the Nantlle Ridge. From here the river flows down through Llanfihangel-y-Pennant, then past Dolbenmaen, and down through woodlands to Llanystumdwy. On the banks of the river at Llanystumdwy is buried the former Prime Minister David Lloyd George who grew up in the village. Just below Llanystumdwy the Dwyfor merges with the Dwyfach and from here enters the joint estuary. The tide can flow around a mile and a half upstream and by the time the river meets the beach, the channel is quite deep. This has been used in the past by ships, but isn't today and the rocks and bars that show at low tide give a good idea as to why.


Afon Dwyfach

The Afon Dwyfach rises somewhere in the gap between Bwlch Mawr, the eastern limit of the Llŷn hills and Mynydd Graig Goch, one of the most westerly mountains of Snowdonia. The Dwyfach drains to the south, whilst the northern side of this valley drains into the sea much closer by in Caernarfon Bay. From here the river flows past Pant Glâs and Bryncir, picking up more water from it's tributaries flowing down from the mountains to the east. After following the A487 road for most of it's journey so far, it then turns off with the B4411 towards Llanystumdwy. Just south of Llanystumdwy, the Dwyfach joins the Dwyfor and heads into Cardigan Bay.

Afon Erch

The marina at Pwllheli is at the mouth of the Afon Erch, which rises some seven miles north on the southern slopes of eastern Yr Eifl, and also gathers water from the Gyrn hills and Bwlch Mawr. These are all part of the highest range of hills on the peninsula and small tributaries from their entire combined southern length all make up the Afon Erch. These tributaries merge just south of Mynydd Carnguwch and then flow as one river past Llwyndyrys, through Rhyd-y-Gwystl near Y Ffôr and on south to Abererch. Here the river turns west and meanders into Pwllheli. In Pwllheli, the Erch meets the already combined Afon Rhyd-hir and Afon Penrhos in the town's marina.


Afon Soch

The Afon Soch's estuary is probably one of the most pictured on the peninsula, with fantastic views across the bay to Snowdon, providing a stunning backdrop. The river starts at Rhos-ddû, between Dinas and Llaniestyn in the centre of the peninsula and flows south through a fairly steep valley to Sarn Meyllteyrn. It then passes the eastern slopes of Mynydd Rhiw and flows through Botwnnog towards Porth Neigwl (Hell's Mouth). At one point the river is only about half a mile from the wide bay of Porth Neigwl, but then turns back in the other direction, past Llanengan and through a sharp glacial gorge to Abersoch on the calmer east coast. The picturesque harbour in the village centre only fills up on high tides, but when it does it can be quite deep and sluice gates have been installed to prevent it running further up the valley in these circumstances.


Afon Rhyd-hir

The Afon Rhyd-hir rises on the south-western slopes of Yr Eifl and then flows down under the B4354 near Pentre Uchaf. From here it flows on to Llannor and then about half a mile around Efailnewydd to where it meets the Afon Penrhos by the A499/A497 roundabout to the west of Pwllheli. Much of the estuary of these two rivers is now not naturally tidal and the water level is controlled by sluice gates on the Cob embankment. The wildlife habitat that has built up in these low lying areas however, has created an excellent haven for wildlife and is now a local nature reserve.


Afon Penrhos

Cors Geirch is a large marshy area in the centre of the peninsula and lies between the hills of Garn Fadryn and Garn Boduan. The Afon Penrhos drains from this marsh to the south, whilst to the north a smaller river/stream also drains from the marsh into the sea at Aber Geirch near Porth Dinllaen. So from here the Afon Penrhos flows through Rhyd-y-Clafdy and south towards Carreg-y-Defaid, where it would have once flowed into the sea. The previous estuary was blocked in by the Victorian embankment that was built to the tramline from Pwllheli to Llanbedrog. The shoals out in the bay are remains of the flat inter-tidal beaches and bars that would have stretched further inland towards Pen-y-Berth. Since it's previous course was blocked the river has been diverted, and now runs northeast towards Pwllheli and runs into the Afon Rhyd-hir by the A497/A499 roundabout to the west of Pwllheli.


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