Two rivers reach the sea at Aberystwyth, The Rheidol and, of course, the Ystwyth, conveniently they both reach the sea in the same place, before the harbour was built they emerged a third of a mile apart but now the Rheidol enters the back of the harbour while the Ystwyth flows to the sea at the harbour mouth. Both rivers run through areas which contain old lead and silver mines so there has been a pollution issue. Special wetlands have now been created to clean the rivers.