:River Arth
{{Use dmy dates|date=April 2022}}
{{unreferenced|date=March 2016}}
{{Infobox river
| name = River Arth
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| image = File:Aberarth and River Arth.jpg
| image_size =
| image_caption = Arth in Aberarth
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| subdivision_type1 = Country
| subdivision_name1 = Wales
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| subdivision_type3 = Counties
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| length_mi = 15
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| source1 =
| source1_location = hills near Bethania, Ceredigion
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| mouth = Cardigan Bay
| mouth_location = Aberarth
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The River Arth is a small river that rises in the hills near Bethania, Ceredigion, Wales, and runs west for {{convert|15|mi|km}} and discharges into Cardigan Bay at Aberarth.
Despite its small size it is one of the few rivers in Britain which has a bore when the incoming tide cause a tidal wave to run upstream. The bore is only a few inches high and it runs only for a short distance upstream; beyond the road bridge in Aberarth the terrain rises steeply, preventing the bore propagating any further.
In the 1970s, the River Arth suffered severe intermittent agricultural pollution from a dairy unit not far from the village but improved pollution control and a change of ownership of the farm rectified that position.
{{Commons category}}
{{coord|52.249|-4.225|display=title}}
{{Ceredigion}}
{{authority control}}
{{Ceredigion-geo-stub}}
{{Wales-river-stub}}