A reconnaissance survey was made of trace metals in surface waters and three aquatic bryophytes (Scapania undulata, Hygrohypnum luridum and Polytrichum commune) in the mid-Wales Ag-Pb mining district. This area is contaminated by heavy metals from past mining. Elevated levels of Ag, Cd, Cu, Pb, and Zn were found in water and plant tissue. All the plants accumulated Ag and the other metals but Scapania appears the most suitable as a plant monitor of Ag-polluted waters.