Venice's 'sacred walls'
The city of the Venetians, by divine providence founded in the waters and protected by their environment, is defended by a wall of water. Should anybody in any manner dare to infer damage to the public waters he shall be considered as an enemy of our country... This act will be enforced forever.A 16th-century edict
Venice’s Lagoon is one of its wonders, a desolate, often melancholy and strange, often beautiful and seductive ‘landscape’ with a hundred personalities. It is 56km long and averages about 8km across, adding up to some 448 sq km; half of it, the Laguna Morta (‘Dead Lagoon’), where the tides never reach, consists of mud flats except in the spring, while the shallows of the Laguna Viva are always submerged, and cleansed by tides twice a day.
To navigate this treacherous sea, the Venetians have developed highways of channels, marked by bricole – wooden posts topped by orange lamps – that keep their craft from running aground. When they were threatened, the Venetians only had to pull out the bricole to confound their enemies; and as such the Lagoon was like an enormous moat, always known as ‘the sacred wall of the nation’.
A lagoon by its very nature wants to turn into land or sea, and in the old days Venice went to great lengths to artificially preserve its ‘sacred wall’ just as it was. In charge of maintaining it was one of the most powerful offices of the Republic: the Magistrato alle Acque.
The Magistrato alle Acque's main concern were the rivers that fed the lagoon, and chief among these was the Brenta, which flowed right in front of the city (where the rail and road bridges now link Venice to the mainland). The Brenta's silt was diverted in the Middle Ages with a levee that sent the flow eastwards, but in the early 1500s, once Venice took control of the terra firma, a more permanent solution was found in the 24km Brenta canal. Diverted from a point near Stra, the river flowed south of the Lagoon into the sea. It also made access easier to all those Palladian villas, where the patricians retreated during the summers of Venice's leisurely decline.
The Lagoon in the 20th century
There still is a Magistrato alle Acque, but it hasn't really measured up to its historic task. The old Venetians knew that mud flats are essential for dampening the high tides. Blithely ignoring all the lessons from the past, the Laguna Morta has been reduced by two thirds since the 1920s with the dredging of shipping channels, including the 1960s' Canale dei Petroli that allows petrol tankers to sail to the petro-chemical works in Marghera. New islands (Sacca San Biagio, Sacca Sessola, Sacca Fisola) were made of dredged landfill, upsetting the delicate balance of Lagoon life.
In the old days the water inside Venice was lower than that in the Adriatic; today it is often higher. Rising sea levels are partly to blame, but there is also evidence that the strong currents created by the deep canals have led to the increase in the number of days of exceptionally high water (acqua alta): in 1983 there were 35 acqua altas, with only one reaching over 110cm. In 1993 there were 44. In 2013 there were 156. The number of serious floods over 110cm increase nearly every year.
Then there are the ingredients in the water itself. The Lagoon is a messy stew of over 60 years’ worth of organic waste, phosphates, agricultural and industrial by-products and sediments – a lethal mixture that local ecologists warn will take a hundred years to purify, even if by some miracle pollution is stopped now. It’s a sobering thought, especially when a handful of very old Venetians still remember when even the Grand Canal was clean enough to swim in.
And then there's the algae
More recently, the Lagoon started sprouting ‘green pastures’ of algae—clogging the lagoon, choking its fish and stinking out many tourists in the summer. No one was sure if the algae epidemic wasn’t just part of a natural cycle; after all, there’s an ancient church on one Lagoon island called San Giorgio in Alga (St George in Algae). Crops of algae are on record in the 1700s and 1800s and at the beginning of the 20th century, at times when the water temperatures were abnormally high because of warm weather.
In 1989, the Magistrato alle Acque joined forces with the Consorzio Venezia Nuova (a group of engineering firms, responsible for the enormous and controversial sea barrier project, MOSE) to clean up the algae. Trying to find a way to dispose of it, the EU sponsored a project to process it (drying it and milling it into a kind of flour, then combining it with fiber) and use it as replacement for pulp in paper. The result is Shiro Alga Carta, manufactured by the Veneto firm, Favini.