The 95 km Sile is a resurgence river. Although modified radically down the centuries, the resurgence area still includes the typical natural elements such as springs ("fontanassi"), pools and marshland, bogs and a dense network of watercourses. As well as the vegetation typical of water-meadows and resurgence pools (Carex, Cirsium, Caltha palustris, Iris pseudacorus), there are also isolated trees and small woods, relicts of the previous coverage typical of the hygrophilous lowland forest facies consisting of poplar, willow, alder, oak, elm, maple etc. The area is of considerable natural importance for the rich insect, reptile and amphibian life and precious fish fauna. It also boasts a large number of nesting and migratory bird species, including the honey buzzard, common buzzard, purple heron, grey heron, little egret and night heron. Archaeological finds from the area show that the resurgence pools were inhabited during the recent Bronze Age.
A strip known as the "spring belt" between 2 and 30 km wide crosses the entire Po plain horizontally, dividing it into a hypothetical "upper" and "lower". This phenomenon is caused by the fact that at the foot of the mountains, meteoric water and water from the Alpine rivers encounter coarse highly permeable soils through which they percolate underground. The groundwater moves very slowly from the mountains to the valley, following the natural slope of the land. In the middle of the plain, the gravely layer becomes thinner, the groundwater encounters clayey almost impermeable soils with a finer grain size and is forced upwards in the "spring belt" area. Here the water gushes spontaneously out of the ground to form pools of limpid drinkable water, often rich in minerals and at a temperature of 12-14°C. The vegetation in this area is diversified, from dry meadows to water-meadows with a marsh-type vegetation and underwater or floating plants.