Only the locals are daring enough to venture into the waters of the Po Delta, where the Po River flows into the Adriatic Sea off the coast of northern Italy. That is – only those among the locals who still remember the position of the river banks and lands which have long since sunk into the water.
Subsidence – the slow and progressive sinking of the ground over time – is a phenomenon which has become very familiar to the inhabitants of the Po Delta region. It has caused the complete submergence of entire stretches of coast over the past 50 years.
The “Isola Bonelli Levante” in Porto Tolle is among the most striking examples of segments of land which have slipped into the sea. A large rice farm, which was in use from the 1970s, has sunk almost 3 metres (nearly 10ft) below sea level and was abandoned in the 1990s.
Another example is the vanishing “Isola Batteria” along the Po della Pila, one of the smaller channels within the wider delta. Once a German military fortification built during World War II on the island which took its name, today it is mostly a lagoon, nearly completely submerged, and can only be reached with difficulty by boat. Just a few buildings remain, reduced to skeletons and semi-submerged ruins.
The murky waters covering the seabed here are shallow. For the boats and kayaks of tourists accompanied by local guides who venture here, the risk of running aground is very real.
Of the old banks of the river, only a few shy reeds break through the surface of the water, showing where until not many years ago you could walk, sow rice or go fishing for hake. Today, those reed beds which once adorned the river bank in abundance seem to be an anomaly as the sea has repossessed land labouriously removed from the waters by centuries of reclamation.
At the mouth of the Po River, where the river meets the Adriatic Sea, saltwater infiltration is reaching worrying levels.
Despite being a natural phenomenon when the freshwaters of the river mingle with the saltwater of the sea, the “salt wedge” – the area in which saltwater has sunk through the subsoil beneath the surface of the land – can spread, particularly in the summer months when there is less rain to help disperse it.
In 2022, which had a particularly dry summer, this salt wedge extended more than 40km (25 miles) inland from the Adriatic Sea. Last year, when there was more rain, the salt wedge spread for 17km (10 miles).
The delta area of the Po River extends for 140 square kilometres (54 square miles) between the regions of Veneto and Emilia Romagna in northeast Italy. Approximately 70 percent of the territory is made up of agricultural land.
The rising salinity of the water is causing damage to the ecosystems along the coast, and to agricultural, livestock and industrial activities, according to a recent report from ARPAE, the Emilia Romagna Agency for the Environment.
There are several factors contributing to rising salt levels in this part of the river, some linked to climate change such as reduced rainfall, drought and the over-consumption of freshwater.
Compounding these issues, the area was heavily mined for methane gas until 1961, when the Italian government halted operations because of subsidence.