Pedrogao dam, Portugal

This dam is part of a system together with the larger Alqueva dam. The artificial basin created by the two of them can contain enough water to supply the whole region for four years without a single drop of rain. Without this engineering masterpiece planned since the Sixties, Alentejo region would be very similar to a desert now. Instead, its economy has changed a lot since the construction of the dam, and now it's a flourishing agricultural region.