The mid-altitude (288 m) Llyn Clywedog Reservoir was constructed in 1967 on the head waters of the River Severn and is 243 ha in size. Its 230 m long concrete buttress dam wall is the tallest concrete dam in the UK with a height of 72 m. Consequently, the maximum depth is 62 m but it has an average depth of 20.1 m deep. Its location, altitude and depth results in cooler water temperatures in the summer doldrums which is probably part of the venues success and it’s reputation as being one the UKs finest fisheries. The reservoir catchment is dominated by acid grassland, coniferous woodland and improved grassland. As such the water has a low alkalinity (86 µEq/l), a light stain (13.5 mgPt/l) and a low conductivity (64 µS/cm).
The trout fishing is run by Llanidloes and District AA with all profits invested back into the venture which includes their own hatchery to stock the reservoir with around 38000 fish each year. They have a large fleet of 33 boats, including a wheelie boat, as of the 2020 season. Their website includes a number of resources to guide the visiting fisher including an interactive map describing the various locations to fish such a large venue, a really handy insect hatch chart for each month of the fishing season as well as a summary of flies which work well at the venue. This is approaching the kinds of information every venue should be aspiring to provide to give the visiting angler the best possible day out. Fulling Mill have a range of Clywedog patterns designed by Russ Simons for the venue.
One of the premier trout fisheries in the UK and Wales’ top fishery.
Last October, with the wild brownie season closed and the prospect of another lockdown looming that would prevent crossing the border into Wales, I decided to head off to fish Llyn Clywedog despite the dire weather forecast. En route the weather didn’t look too bad and I was hopeful that it would be one of those days when the MetOffice had got it wrong. As I drove into Llanidloes the rain started and intensified as I drove the final few kilometres to the reservoir. The weather was so wild that I didn’t stop to marvel at the concrete buttress dam which is the tallest concrete dam in the UK, with a height of 72 metres (236 ft) and a length of 230 metres (750 ft). The fishing is run by the local Club Llanidloes and District AA with all proceeds put straight back into the fishery. The club rear their own fish in a series of cages set in the reservoir. This ensures the stocking of top quality fish at a reasonable day ticket price. Along with a high quality fleet of 35 boats this is purported to be one of the premier trout fisheries in the UK and Wales top fishery. I was keen to find out for myself if this was the case.
The checkin was fast and COVID secure and the boat was very clean, well maintained and one of the best I have used in some time. With the wind hammering down the reservoir from the NE and the whole fleet of boats drifting from Eblid down past the cages towards the sailing club I decided to setup in the relative calm of Cwn Coch bay and explore the bank down to Eblid. The wind was swirling into Cwn Coch producing a series of foam/scum gyres and bubble lines so I setup with some hoppers and a crane fly and set about exploring these features. There didn’t seem to be much action, but careful observation showed that there were a few fish sipping down insects collecting in the foam. One cruised past the boat and it was huge. The issue was they were hard to spot and with feeding high up in the water had a small field of view, I was going to have to be patient. I spotted one on a feeding line and manoeuvred the flies into the path. It approached the daddy and sipped. This is where a season spent chasing lightning fast wild brownies turned out to be a dis benefit as I didn’t wait long enough for the fish to suck the fly down and struck too soon literally pulling the fly from its mouth … bugger! The dark skies turned blue as I berated myself for my impatience. With nothing else happening for a while, I drifted down to Eblid along the shoreline in a bucking boat straining at the drogue tethers a few times without success.
Llyn Clywedog rainbow trout 
Anglers on Llyn Clywedog 
Llyn Clywedog office and moorings from Cwn Coch 
Llyn Clywedog rainbow trout
I could see bubble lines further out from the shore so decided to give those a go drifting from just beyond Cwn Coch back towards the moorings. That was where the action was, with a silver bar emerging from depth to take a hopper pattern. This was a big fish that fit across the bottom of the net and up the side and even with a 9’6″ 7 weight rod took some serious taming before it hit the net. I suspected that given the depth it came from that the fish were feeding at depth so switched from dries to wets. This is far from my ideal fishing method but you have to fish to the conditions.
Having fished dries all season with a 5 wt 9’00” soft action rod my arm was struggling to hurl weighted taddies, dancers and fry patterns on a heavier line and rod in the howling gale but needs must. However, this turned out to be a winning formula with fish after fish hammering the flies and fighting for ages. I was glad I was fishing barbless flies which came out of the fishes mouth during the netting process and I was releasing all my fish as leaning over the edge of the bucking boat to photograph the fish was more than a little scary, more so as I was fishing on my own. Cold, wet, battered and aching I left late afternoon very satisfied having had a good day of fishing with little time to think about anything else but fishing, boat and drogue management in the adverse squally conditions. Result!
While on this occasion I opted to do a quick day trip, simple options for an overnight include the Hafren Forest Bunkhouse and I believe that the yacht club has a space or two for camping. The site is managed by Severn Trent Water and has basic facilities in keeping with the surroundings. Here are some activities for the family while you explore the reservoir:
- Sailing club to launch craft
- Hafren Forest walks
- Bryntail lead mine buildings
- Visit the Clywedog Osprey hide or watch them on webcam
- Visit the Glaslyn Nature Reserve to see the cotton grass and heather
- Walk the Glaslyn and Bugeilyn audio trail
- Walk to the source of the River Severn
- Visit Bryntail Lead Mine Buildings
See the things to do for Llyn Bugeilyn as well as these contain further suggestions.
Tight Lines
Greg