The territory of Casalvieri is crossed by the Melfa river that flows in a gorge for 13 km between high rock walls, in picturesque landscapes with the white rock carved by the water, before entering the plain of Roccasecca and joining the river Liri.
The gorges of Melfa are a site of community interest and a special preservation area (SIC-SPA).
The Melfa arises from a rock of Monte Petroso in the Valle di Canneto, in the municipality of Settefrati.
It is said that its name is connected to that of the pagan goddess Mefiti and, in the area of the source, the remains of a pagan temple of the IV century BC have been found.
Some of its remains can be found in the crypt of the Sanctuary of the Madonna di Canneto which each year receives over 60,000 pilgrims in the month of August.
From Settefrati the watercourse passes through a gap in the mountains giving rise to gorges, caves and canyons of extreme beauty, such as the Marmitte dei Giganti.
In the Casalvieri-Roccasecca stretch, the Melfa receives the waters of the Rio Inferno, Rio Pietraia and Rio Contieri which form waterfalls of 15 meters. Rio Inferno, Rio Pietraia e Rio Contieri che formano cascate di 15 metri.