Cors y Llyn National Nature Reserve, near Builth Wells

What's here


Cors y Llyn means “bog of the lake” and the expanse of bog and fenland at this National Nature Reserve was once a lake.

One of the best wildflower-rich meadows in mid-Wales is at the reserve entrance and some of the trees in the boggy section are over 100 years old even though they are only a few feet tall!

The short accessible walking trail goes alongside the wildflower meadow and along a boardwalk past the stunted forest.

Walking trail

The walking trail is waymarked and starts from the car park.  

Waterproof shoes or boots are recommended for visits between autumn and early spring as water can seep up through the boardwalk.

Please keep to the boardwalk and paths – there are areas of deep open water and deep steep-sided pools covered with floating vegetation.

Cors y Llyn Walk

  • Grade: Accessible
  • Distance: ¾ mile/1.3 kilometres

Just beyond the gate from the car park, the path goes alongside the wildflower meadow and then skirts around a pond where there is a bench to enjoy the view.

The boardwalk then winds through the swampy woodland and past the stunted forest, before a gentle incline back to the car park.

National Nature Reserve

Cors y Llyn is a National Nature Reserve.

National Nature Reserves are places with some of the very finest examples of wildlife habitats and geological features.

There are over 70 National Nature Reserves in Wales.

Find out more about National Nature Reserves.

Wildflowers and plant-life

Wildflower meadow

The two basins which form the core of the reserve were originally carved out by glaciers during the last Ice Age and filled with meltwater.

Over thousands of years, they gradually became choked with vegetation, stones and earth, to create the rich, mixed habitats at the reserve today.

The basins support a range of acid-loving plant-life, with abundant bog-mosses, ling, cranberry, cross-leaved heath and the insectivorous round-leaved sundew. At the edges, there are patches of bog asphodel.

The southern basin has its own distinctive character: the Scot’s pine here is severely stunted, Scandinavian style, because of the water-logged peat.

A ribbon of birch wood and fen surrounds the bog.

Over 100 flowering plant species have been recorded in the meadow, including heath-spotted orchid, carnation sedge, lesser skullcap and sneezewort.

Seasonal highlights


Look out for pale-pink patches of colour in the meadow – these are the cuckoo flower which is one of the first flowers to bloom in very early spring.

A host of spring flowers follow this early display, including the heath spotted orchid, marsh violet and meadow thistle.


The meadow is at its best in summer with its wealth of wildflowers attracting lots of butterflies on warm, still days.


There is a colourful display of damselflies and dragonflies near the pond in summer, too, including some larger ones like the emperor and the southern hawker.

If you’re in luck, you might have the rare privilege of spying a hobby, catching these insects on the wing.

Look out for pied flycatchers, redstarts and wood warblers – the Welsh oak woodland summer visiting trio.


The brightly coloured mosses and lichens will help to brighten up even the dullest of days.

Listen out for the croak of the common frog as you walk past the damper areas.

You may also catch sight of a common toad and palmate newt.


Birds that visit the reserve during winter include woodcock and snipe.

Accessibility information

Boardwalk at Cors y Llyn

The paths are level and mesh-covered paths and the boardwalk is accessible.

There are seats and passing places for wheelchair users.

Closures and diversions

Please note:

  • Sometimes we need to close or divert trails for your safety whilst we undertake maintenance work
  • Occasionally we may have to close a site in extreme weather, such as high winds or snow and ice due to the risk of injury to visitors or staff
  • Please always follow any instructions onsite and make sure you follow any temporary diversion signs in place

How to get here


Cors y Llyn is 3½ miles north west of Builth Wells.

It is in the county of Powys.

Ordnance Survey map

Cors y Llyn is on Ordnance Survey (OS) map 200.

The OS grid reference is SO 016 556.


Take the A470 from Rhayader towards Builth Wells. Immediately after driving through the village of Newbridge on Wye, turn right onto a minor road (the former A470 which runs parallel with the new A470 road south towards Builth Wells). Continue along this road for approximately 1½ miles, go over a stone bridge and take the next turn right opposite a cottage with dormer windows. Follow this narrow lane for about ¼ mile, proceed with care through a privately-owned yard and head for the far left hand corner from where the road continues out of the yard and on to the Cors y Llyn car park.

Public transport

For details of public transport visit the Traveline Cymru website. 


Parking is free of charge.

Overnight parking is not permitted.

Contact details

Tel: 0300 065 3000


Related document downloads

Other places in Mid Wales

Last updated