The Obernaustausee is located in Siegerland about 9 km (as the crow flies) northeast of Siegen and about 2.8 km (as the crow flies) northeast of the city center of Netphens on the southwestern roof of the Rothaargebirge. It extends immediately to the east of Brauersdorf, a northeastern district of Netphen.
The reservoir is dominated by the mountains Alte Burg (632.9 m above sea level), the location of a former refuge and cult site from the La Tène period around 500 BC. Chr., And Sanktkopf (606 m). In addition, around the Obernautalsperre there are the mountains Leyberg I (512 m), Scharn (496.6 m), Leyberg II (498.9 m), Kemerling (477.4 m), Nollenkopf (479.1 m) and something from the dam is the broad mountain (629.2 m). [1]
The dammed rivers are the small creeks Obernau, which rises between Alter Burg and Breitem Berg and flows a few kilometers below the dam into the Sieg, which flows in from the east, and the Nauholzbach, which swells near the Hohenroth forester's house and flows into Obernau. There are pre-locks at both tributaries. In addition, a few smaller tributaries flow into the reservoir, including the Burbach.