The Olef Dam (German: Oleftalsperre) is located in the vicinity of the Eifel National Park near Hellenthal within the High Fens-Eifel Nature Park in the county of Euskirchen in the German state of North Rhine-Westphalia.

The Olef Dam was built between 1954 and 1959 for two purposes: to protect the surrounding municipalities from floods; and to supply drinking water.

The dam had to be reinforced twice because large variations in temperature and shrinkage of the concrete produced greater internal stresses than were foreseen, leading to cracks.

The initially open downstream side was sealed in order to limit the temperature variations.

In early April 2007 the downstream face of the dam was decorated by artist, Klaus Dauven, with high pressure cleaners as part of Project Wildwechsel.