The 17 dams in the Harz block a total of twelve rivers. Because the Harz is one of the regions of Germany that experiences the most rainfall, its water power was used from early times. Today the dams are primarily used to generate electricity, to provide drinking water, to prevent flooding and to supply water in times of scarcity. Modern dam-building began in the Harz with the construction of the Söse Valley Dam, which was built between 1928 and 1931. The dams of the Upper Harz lakes are some of the oldest dams in Germany that are still in operation.