From its source to its discharge in Conwy Bay it is 55 kilometres (34 mi) long and drains an area of 678 square km.

To the west, the catchment is underlain by older Cambrian rocks which are harder and the landscape is, as a consequence, more dramatic with high craggy hills and mountains, through which the river falls in cascades and waterfalls.

The shoreline is supported by natural rock, in addition to boulder clay cliff, sand dune, salt marsh and woodland.

[7] The scattered communities along the Conwy valley have ancient traditions with archeological evidence of habitation back to the Stone Age.

Much of the Conwy valley was laid waste in the Wars of the Roses by the Earl of Pembroke, under the orders of Edward IV, the Yorkist king, following a Lancastrian attack on the town of Denbigh in 1466.

[10] The Conwy is noted for its salmon and sea trout, although increasing acidification in the second half of the 20th century, especially in the poorly buffered upland waters has significantly impacted upon their spawning success.

The construction of an artificial fish pass in the 1990s to allow migratory salmonids access to the river above Conwy falls was intended to help mitigate the effects of acidification.

However, problems with resupply in the event of siege and its destruction by Llywelyn ap Gruffudd, Prince of Wales in 1263 to prevent it falling into King Edward's hands, led to a new castle being built across the water in Conwy town.