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About this place
Llyn Cwm Corsiog is a small mountain lake in Gwynedd, north Wales, tucked into the uplands of Eryri (Snowdonia). It sits high above the village of Tanygrisiau, close to Blaenau Ffestiniog, at roughly 53.004° N, 3.993° W. It rewards walkers and anglers who are happy to earn their view on foot.
Where is Llyn Cwm Corsiog?
The lake lies in a glacial hollow (a Welsh cwm) on open, grassy slopes above Tanygrisiau. Its elevation is given as about 520 m, or around 1,720 ft, and its surface covers some 7 acres, just under 3 hectares. This is a tarn rather than a large reservoir, which is exactly why it feels so quiet.
How do you get there?
No road reaches the water. The walk starts in Tanygrisiau and takes about an hour and a half, according to local angling descriptions. The terrain is upland pasture, so expect damp ground and quickly changing weather. Wear sturdy boots, pack waterproofs, and bring a map or offline navigation, because mobile signal in the hollows is unreliable.
What can you do here?
Fishing is the main draw. The Cambrian Angling Association, based in Blaenau Ffestiniog, manages the water. It holds wild brown trout that are plentiful, rise freely to the fly, and typically reach about three quarters of a pound. Any fishing method is permitted.
If you don't fish, the lake works as the destination of a hill walk: open Eryri slopes, silence, and a place to rest before heading back down.
When is the best time to visit?
Anglers rate the early season highest. By midsummer, dense weed covers parts of the lake and makes some areas unfishable. Later in the year you can still do well with a floating line and dry fly, casting into clear gaps between the weed. Walkers should pick a dry day with good visibility, when the path is less boggy.
Do you need a permit?
Fishing requires a Cambrian Angling Association ticket. Since 2024 it can no longer be booked through The Fishing Passport. The club's website, cambrianangling.com, lists local outlets. Sort this out before you set off, as nobody sells tickets on the hill.
Frequently asked questions
Can you drive to Llyn Cwm Corsiog?
No. You walk from Tanygrisiau, which takes around 90 minutes one way.
How big is the lake?
About 7 acres (just under 3 ha), at around 520 m above sea level.
What fish live there?
Wild brown trout, usually up to about three quarters of a pound.
Can I fish without a club ticket?
No. The Cambrian Angling Association controls the fishing, and its website lists where to buy tickets.
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