The River Usk, Afon Wysg in Welsh begins life as a peaty trickle on the slopes of Fan Brycheiniog in the Brecon Beacons National Park. It flows for around 100km (60 miles) east and then south-east through Abergavenny and the eponymous town of Usk to the Roman legionary fortress of Caerleon and the Bristol Channel at Newport. It is the deepest river in the British Isles at its mouth and has the second largest tidal range in the world after the Bay of Fundy in Canada.
Most of the catchment is rural with farming the dominant industry. The River Usk attracts anglers, canoeists, boat users, walkers and naturalists. It links historic towns like Brecon and Crickhowel, Abergavenny and Usk and for much of its length it is shadowed by the Monmouthshire and Brecon canal. Its upper reaches are entirely within the Brecon Beacons National Park. It is one of the principal salmon rivers in Wales and is also renowned for its wild brown trout. The catchment also provides habitat for otters, water voles and native crayfish, and the headwaters have seen a resurgence in Red Kite numbers
The climate is mild and wet (with up to 3,000 mm of rainfall on the mountain peaks), providing high yield for the reservoirs in the upper catchment. The rainfall rapidly runs off the Old Red Sandstone rocks and thin soil cover, resulting in the flood plains becoming inundated during periods of heavy rain.
There are many recorded floods on the river:
"The Llanfaes Bridge, constructed in 1563 ....... replaced one built 35 years earlier which had been destroyed by the first recorded major flood in Brecon."
A letter from Wales informs us of the dreadful inundation of the river Usk the latter end of November; by which vast numbers of cattle of all kinds, stacks of hay, and ricks of corn, were washed away, and several farmers thereby utterly ruined. The waters were up to the first stories of the houses.