No, it’s not the rising water. (“So go get boots,” says the mayor.) It’s tourism. 21 million visitors poured into and out of Venice in 2007. The number of hotels and guesthouses has septupled in the last ten years; vegetable sellers, hardware stores and other such urban necessities are being priced out; the cost of living, especially housing, climbs steadily; the population is down to 60,000 and shrinking. “Who will be the last Venetian left?”