The River Ystwyth (Welsh: Afon Ystwyth in Welsh) is a river of mid west Wales. It has its source to the west of Craig Goch Reservoir in the upland moors also known as the desert of Wales.
The river flows generally westwards before draining into Cardigan Bay at Aberystwyth where it shares the harbour with the River Rheidol. The Ystwyth valley is now sparsely populated with only a few towns and villages such as Yspyty Ystwyth, Cwm Ystwyth, Pontrhydygroes, Llanilar and Llanfarian. In previous centuries, however, the Ystwyth valley was relatively densely populated because of the mineral wealth that existed there. Silver, Lead and Zinc have been mined in the valley since Roman times and this activity reached its peak in the 18th century. The largest of the very many mines was Cwm Ystwyth Mine. It is reputed that the average age at death of the miners in Cwm Ystwyth was 32, largely because of acute lead poisoning. There is now no active metal mining in the Ystwyth valley.
The River still carries elevated levels of lead, zinc and silver in its water, mostly from seepage from abandoned mine tailings and discharges from mine adits. Away from the abandoned mine workings, the river valley is one of the most beautiful in Wales with steep wooded banks carrying a crystal clear water. It is especially beautiful in Autumn. The autumn also tends to bring large numbers of visitors to parts of the upper valley where Magic mushrooms are allegedly found in substantial quantites growing wild.