The Afon Ysgir is a short river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 which rises on the southern slopes of Mynydd Epynt

Mynydd Epynt

Mynydd Epynt is an upland area of Mid Wales within the county of Powys, Wales. It is bounded to the south by the upper section of the valley of the River Usk, to the north by that of the Afon Irfon and to the east by the valley of the River Wye. Its western boundary is less distinct but lies...

 in Powys

Powys

Powys is a local-government county and preserved county in Wales.-Geography:Powys covers the historic counties of Montgomeryshire and Radnorshire, most of Brecknockshire , and a small part of Denbighshire — an area of 5,179 km², making it the largest county in Wales by land area.It is...

, Wales

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

. The tributaries known as Ysgir Fawr and Ysgir Fechan flow past the hamlets of Pont Rhyd-y-berry and Merthyr Cynog

Merthyr Cynog

Merthyr Cynog is a hamlet and a community in the county of Powys in mid Wales.The Welsh name signifies the 'shrine of Cynog'. The church, a place of pilgrimage, is dedicated to Saint Cynog, a son of Brychan Brycheiniog...

 to combine at Pont-faen and continue past the village of Battle to join the River Usk

River Usk

The River Usk rises on the northern slopes of the Black Mountain of mid-Wales, in the easternmost part of the Brecon Beacons National Park. Initially it flows north into Usk Reservoir, then east by Sennybridge to Brecon before turning southeast to flow by Talybont-on-Usk, Crickhowell and...

 at Aberyscir

Aberyscir

Aberyscir is a village in the Welsh county of Powys, in mid-Wales....

.

Its upper reaches are within the military training area of SENTA

Senta

Senta is a town and municipality on the bank of the Tisa river in the Vojvodina province, Serbia. Although geographically located in Bačka, it is part of the North Banat District...

, the British Army's Sennybridge

Sennybridge

Sennybridge is a village in Powys, Mid Wales, situated some from Cardiff and from Swansea. It lies west of Brecon on the A40 trunk road to Llandovery, at the point where the River Senni flows into the Usk...

 Training Area.

Near its mouth is a motte

Motte-and-bailey

A motte-and-bailey is a form of castle, with a wooden or stone keep situated on a raised earthwork called a motte, accompanied by an enclosed courtyard, or bailey, surrounded by a protective ditch and palisade...

, the historic church at Aberyscir and east of the river, the Roman fort of CICVCIVM or Brecon Gaer

Y Gaer, Brecon

Y Gaer, Brecon is a Roman fort situated near modern day Brecon in Mid Wales, United Kingdom.Y Gaer is located at .- History :...

. Along with othe tributaries of the Usk, the river is designated as a special area of conservation

Special Area of Conservation

A Special Area of Conservation is defined in the European Union's Habitats Directive , also known as the Directive on the Conservation of Natural Habitats and of Wild Fauna and Flora...

 or 'SAC' for various species of fish including lamprey

Lamprey

Lampreys are a family of jawless fish, whose adults are characterized by a toothed, funnel-like sucking mouth. Translated from an admixture of Latin and Greek, lamprey means stone lickers...

, the twaite shad and the European bullhead

European bullhead

The bullhead is a freshwater fish that is widely distributed in Europe, mainly in rivers. It is a member of the Cottidae family, a type of sculpin...

.