The River Ystwyth is a river in west Wales. It starts in the hills between Rhayader and Ysbyty Ystwyth and flow into the sea at Aberystwyth. Although the river looks very clean, it has high levels of some metals such as lead, zinc and silver. These metals poison a lot of the wildlife so that only a few things live in some of the river. These metals get into the river from old lead mines. Nobody uses the mines any more but the waste material left behind still has lots of metal in it and this dissolves in rain and gets into the river.