Some scholars have theorised that the lake level has been artificially lowered since the Etruscan era, but the Farnese tunnel is the only one currently known to archaeologists.

The conduit, whose vault is supported by courses of bricks, receives the waters from a lock dating back to the Farnese era, runs for about 400 meters to exit on the opposite side of the mountain ridge, in the Vicano river gorge.

The waters of the outflow, which have been below the threshold for a couple of years due to very low rainfall, flow out of the lake through an artificial circular-section tunnel built in the 1990s.

Since ancient times, the construction of the tunnel has allowed a significant lowering of the water level, transforming part of the lake, and especially the entire northern area of ​​the caldera (the so-called "Pantanacce") into an agricultural.

The geography of the lake that we can see today is therefore different from the original one: Mount Venere, born following the last phase of activity of the Vicano volcano (ended 90,000 years ago) which now rises in the northern part of the basin giving it the characteristic "horseshoe" shape, was probably a peninsula and the surface area of ​​the body of water was almost double that which can be measured today.