Birds in the area include bullfinch, kingfisher, linnet, reed bunting, skylark, and song thrush.

The valley is at risk of flooding between Cross Inn and Pontyclun and the river is liable to overflow its northern bank along its one-and-a-half-mile (2.4 km) length downstream from the main A4119 (Tonypandy to Cardiff Bay (Bae Caerdydd)) road at Talbot Green (Tonysguboriau) to Pontyclun, providing a wetland wildlife habitat.

The Afon Clun, a major tributary of the River Ely, drains an area of 12 square miles (31 km2) to the north-west of Cardiff in south Wales.

The lower northern slopes of The Garth form the boundary with Rhondda Cynon Taf, about half a mile (800 m) north of the Clun's source.

[7][8] The Clun then flows beneath the main A4119 (Tonypandy to Cardiff Bay) route about 50 metres (164 ft) south of the roundabout by Glamorgan Vale Retail Park, Talbot Green.

Immediately past the bridge, 14 miles (23 km) from its source, is the Afon Clun's confluence with the River Ely, which heads south, east to Miskin, almost encircling Pontyclun, then south on its way to Cardiff, where it flows into Cardiff Bay by Penarth Marina, which flows into the Bristol Channel.

The eastern part is the prominent wooded slopes of the Taf Valley – a backdrop to the Treforest Industrial Estate.

SLAs are identified using the Countryside Council for Wales' LANDMAP criteria, considering factors such as prominence, spectacle (dramatic topography and views), unspoilt areas (pre-industrial patterns of land use), remoteness and tranquility, vulnerability and sensitivity to change, and local rarity of landscape.

[6] The Clun flows through, and close to, several areas defined in the UK Biodiversity Action Plan (BAP) as 'Areas of Ecological Significance'.

Birds of 'conservation concern' recorded in surveys of the area are bullfinch, kingfisher, linnet, reed bunting skylark, and song thrush.

[9] Two companies in the area around the Afon Clun valley are regulated by a system known as Integrated Pollution Control (IPC).

"[9] Since the end of coal mining in south Wales, the Afon Clun gradually returned to the condition in which it was before the Industrial Revolution,[16] although it has been polluted several times since then.

[13] Nant Myddlyn, a tributary on the Clun, suffered from a diesel spill near Llantwit Fardre, in early 2008 CE, which was raised at the Senedd.

An effective effluent treatment plant was recommissioned to solve the discharge problem and water quality soon returned to RE2, until the works' closure in 2002 CE.

Since Coal Products' Cwm Coking Works closed, water abstraction from the Afon Clun area is minimal.

[9] The Clun is liable to overflow its northern bank for about one and a half miles, between Cross Inn and the River Ely.

From the end of the last ice age, between 12,000 and 10,000 years before present (BP), mesolithic hunter-gatherers from Central Europe began to migrate to Great Britain.

They would have been able to walk between Continental Europe and Great Britain on dry land before the postglacial rise in sea level around 8000 BP.

Together with the approximate areas now known as Brecknockshire, Monmouthshire and the rest of Glamorgan, the Afon Clun Valley was settled by a Celtic British tribe called the Silures.

[22] There is a group of five round barrows, near the river's source at the top of The Garth, thought to be Bronze Age, one of which supports a trig.

[25][26] Caerau Hillfort was the subject of a forgery in a book called 'Gwentian Brut' in The Myvyrian Archaiology of Wales, edited by Jones, O.; Williams, E.; Pughe, W.O.

The forgery was fabricated by Edward Williams Iolo Morganwg) while he was one of the editors of Myvyrian Archaiology; it suggested that Caerau Hillfort was the site of the "Battle of Rhiwsaeson" in 873 CE.

Charcoal to heat the furnaces was probably derived locally, from "Cloune Park" — mention is made by Rice Lewis in his 'A breviat of Glamorgan' (1595 and 1600) of the destruction of the forests of Garth Maelog and Allt Griffith because of the ironworks.

A methane gas explosion on bank holiday Monday, 2 June 1941, killed four men — Ernest Evans (Banksman), Noah Fletcher (Winding Engineman), John Gregor (Manager), and David Thomas (Switchboard Attendant) — and destroyed most of the surface buildings.

[31] Improvements to the road network, in particular the A4119 linking the Rhondda Valleys to the M4, through Tonyrefail and Talbot Green, brought development pressure to the area around Llantrisant.

[9] This development brought further pressure on the road system, which led to the revival of the 1989 plans for the Church Village bypass.

[34] An Environmental Constraints Plan has been compiled and updated from ecological surveys of 1999, 2000, 2003, 2004, 2006 and 2007, with a view to minimising the effect of the bypass scheme.

Findings from the surveys show the presence of bat, badger, dormouse, otter, great crested newt and the marsh fritillary butterfly.