This lake did not exist. It was born in 1963 from a barrage on the Tiber, built to regulate the water flowing out of lake Corbara and use it to produce power. A hydroelectric work, in other words, and nothing else: nature had no part in it. Then the basin began to silt up, the depth dropped to a few dozen centimetres, and the birds arrived.
What to see
Thousands of migrating birds took to stopping here, and at that point the local authorities, the WWF and the electricity company did the only sensible thing: they turned the reservoir into a protected oasis. Today the area covers about nine hundred hectares in the Tiber valley, among reed beds, shallow water and riverside woods.
The lake carries the name of Alviano because it is here that the river was dammed, but the oasis extends over several municipalities and its equipped entrance is on the other side of the water, in the territory of Guardea, in the hamlet of Madonna del Porto. Those who come from Alviano see the basin from the side of the dam and the hill town.
Visiting
The oasis is run by the WWF, with guided visits, hides and seasonal opening: you go above all in winter and spring, when the birds are there, and it is worth checking hours and access before setting off. Half a day.
Our editors' tip
Keep in mind that you are looking at a piece of infrastructure that went wrong. The lake was meant to stay deep and clean, it filled with silt and turned into a marsh: from an engineering point of view it is a failure, from a heron's point of view it is the best thing that has happened to the Tiber in a century. That happens too.