Around 1900, mining shaft depths of 1,000 metres were attained. But the cost of mining at greater and greater depths continued to rise. As the same time the industry had to compete with other metal mining areas at home and abroad in an era of improving transportation. Overexploitation during the First World War and plummeting metal prices during the Great Depression caused, at its peak, a great wave of closures, as large mines in Clausthal-Zellerfeld, Bockswiese and Lautenthal had to shut down. In Bad Grund, however, mining in the Upper Harz continued until 1992, but it only needed to use a small fraction of the facilities of the Upper Harz Water Regale.