Dawn breaks over the Venetian Lagoon in breathtaking silence. In a few hours, Piazza San Marco will fill with great swirls of pigeons and tourists bearing selfie sticks, and the Grand Canal will be as busy as a peak-hour freeway. But at this hour, on a jetty off the island of Burano, all is calm, and there’s barely a ripple on the water as we set off with Lele D’Este in his shabby fishing boat. “It’s so beautiful here,” D’Este says as he kills the engine a few kilometres north of Burano and throws a net into the opaque water. “It’s truly heaven.”

Caught between the Italian mainland and the Adriatic Sea, the 550-square-kilometre lagoon stretches from Jesolo in the north-east to Chioggia at its southern tip. Dotted with 118 islands, it’s a marvel of nature and human endeavour, having evolved from the estuarine lagoons of the Roman era well before Venice emerged as an ambitious maritime power in the 10th century.

Like the storied city, the lagoon is recognised as a World Heritage site of critical environmental significance. Flooded by the salty waters of the Adriatic, its shallow marshes are a haven for marine life and birds, but they’re increasingly vulnerable to rising sea levels, pollution, dredging and erosion.

D’Este, 58, has been fishing these waters since he was a teenager. Apart from a few cefalo, the lagoon’s grey mullet, the fish aren’t biting this morning. He slips overboard, gathers a few crabs and mussels from the muddy shallows, and we head home to Burano.