Free On the Shores of the Mediterranean by Eric Newby Page A

of the Waters had left open centuries ago, having sealed off the others after yearsof trial and error, by doing so preserving a delicate balance which allowed Venice to function both as a city and a great seaport. Now, for six hours, the tide would flow into the Lagoon, which is not what it appears to be – a single simple expanse of water – but is made up of three distinct basins, each separated one from the other by watersheds known as the spartiacque , spreading through its main arteries and myriad veins, channels so small that no chart shows them, and scouring and filling the canals of the city itself. Then, at the end of the sixth hour, when it was at the full, the tide would begin to run out, loaded with the effluent of the industrial zones, which sometimes includes dangerous quantities of ammonia and its by-products of oxidation, phenol, cyanide, sulphur, chlorine, naphtha, as well as oil from passing ships and boats, all the liquid sewage of Venice, the peculiarly filthy filth of a city entirely without drains, a large part of the solid ordure produced by its inhabitants, and at least a part of that produced by Mestre and Marghera, together with vast quantities of insoluble domestic detergent. One of the more awful sights in the Lagoon used to be a mud bank at Marghera with mountains of ordure rising from it, preserved, presumably for all eternity, or until they burst, in plastic bags. There they waited for an exceptionally high water, an acqua alta , to distribute them over other distant parts of the Lagoon, with thousands of gulls, apparently unable to penetrate them with their beaks, hanging frustratedly over them. All because a large incineration plant, built in the Second Industrial Zone, failed to work.
    Twenty years ago the only fish of any size that was indigenous to the Lagoon and which reproduced itself in it was something called the Gò ( Gobius ophocephalus ), which nested in the mud on the edge of the deep canals. All the others were caught in the open sea and penned in the valli at the northern and south-western ends of the Lagoon. Mussels were also cultivated. Whether it issafe to eat any of these fish today must be questionable. There is no need any more for the Commune to display the warning against swimming on the door of the crumbling open-air swimming place on the Zattere, the long waterfront in Venice facing the Giudecca Canal. It is only too obvious.
    The Adriatic performs this operation of filling and emptying the Lagoon four times every twenty-four hours over an area that used to be roughly thirty-five miles long and up to eight miles wide, but is now much less because of infilling and the construction of new valli . That is except during periods of what Venetians call la Colma or l’acqua alta , high water.
    Even though the moon was nearly full there would be no acqua alta on this particular night. Acqua alta is not dependent on the tide itself being exceptionally high, or even high. It occurs when the barometric pressure falls sufficiently low to allow the level of the Adriatic to rise on what is a very low coastline, and when the strong, warm, south-westerly sirocco blows up it. If the barometric pressure is low enough and the sirocco is strong enough at the time when the ebb is beginning in the Lagoon, the water is penned inside it, unable to get out, and when the next tide begins to press in through the three entrances, the Porti , and is added to the high water already there, the natural divisions between the three basins of the Lagoon, the spartiacque , cease to exist and Venice and many other islands, inhabited and uninhabited, are flooded. Other factors can make the acqua alta even higher – heavy rain, a full moon, something called the seiche , the turning of the Adriatic on an imaginary pivot – but the sirocco and a low barometer are the two indispensable conditions.
    This is not a new phenomenon. The records of the acqua alta from the thirteenth century onwards are full of