The Nature Reserve of the Lake of San Domenico is about 30 hectares wide. It is made up of two areas: the Lake of San Domenico, with the hermitage of San Domenico, a pic-nic park and the sources of the Sagittario river; and the Lake of San Pio, smaller than the first one and next the borough of Villalago.
The Nature Reserve was set up in 2005 to protect its valuable flora and fauna. In the crystal clear lake waters there are trout, pike and brass. Wildfowl and a flock of white geese live there. Marsican bear, Apennines wolf, deer and other animals are the fauna of the steep mountains and woods that surround the lake. It is possible to hike from the Lake to Villalago.