Recreational gold mining and prospecting has become a popular outdoor recreation in a number of countries, including New Zealand (especially in Otago), Australia, South Africa, Wales (at Dolaucothi and in Gwynedd), in Canada and in the United States especially. Recreational mining is often small-scale placer mining but has been challenged for environmental reasons. The disruption of old gold placer deposits risks the reintroduction of post gold rush pollution, including mercury in old mining deposits and mine tailings.