Driving east from Zwettl, one comes to the 4.5 square kilometre Ottenstein Resevoir, somewhere well equipped to take tourists as one sees from the enormous car park at the site. The dam was created in the last days of the Austro Hungarian Empire and the hydro electric facilities there are due credit - one can see the original turbines which were in action until 1970. In its present state, the reservoir was created in the 1950s.
Ottenstein is the furthest upstream and also the largest of the three reservoirs along the Kamp River. It offers landscapes of striking beauty and a host of popular recreational activities. The deep inlets along the lake shore are reminiscent of Scandinavian fjords, a land form that is not really typically Austrian.
One can rent an electric boat which allows access to some of the place hard to get to on foot. For those interested in fishing, pike, carp, perch, zander, tench and trout are available in the lake. Fishing licences are available from the Ottenstein Forestry Office (phone: +43 2988 6530) and from the Niedernondorf farm and forestry operation (phone: +43 2826 7578).
Near the northern shore we find the shingle covered cone and hipped roofs of Ottenstein Castle. Of particular interest is the Romanesque castle chapel with vaulted ceilings decorated with monumental frescos dating back to about 1170.