Lago di Fiastra, Reservoir in Monti Sibillini National Park, Marche, Italy.

Lago di Fiastra is a reservoir in the province of Macerata, created in 1955 by a dam on the Fiastrone river. The water is opaque and deep teal-green, held in a valley bordered by steep hills. A pale band of exposed stone and earth lines the left and lower shores, widening into a small flat beach near the bottom right, while a rounded wooded slope descends directly to the water on the upper right.

Construction of the dam began after World War II and finished in the mid-1950s to generate electricity and supply water to surrounding communities. Since that time the basin has shaped the landscape of the southern park and continues to serve regional energy needs.

The lake is known for the Triathlon dei Monti Sibillini and for sport fishing competitions held on its waters. A dirt track starting at the dam leads to the Lame Rosse, rock formations reached on foot from the reservoir.

Several parking areas are located along the eastern shore, where barbecue spots, grassy areas for relaxing, and simple boat rental stands are also available. Walking trails circle parts of the shoreline and connect the different access points, and sturdy shoes are helpful especially in the forested sections.

When water levels drop, foundations of old farmhouses that stood here before the valley was flooded occasionally emerge. These sunken ruins recall the settlements that had to give way to the dam project.