A few miles offshore from Caorle, Cavallino-Treporti, Lido di Venezia, and Chioggia, the typical sandy floor leave room for a completely diverse environment teeming with beachrock outcrops distributed discontinuously along about 30 km.

These are the Tegnùe of the Upper Adriatic, known since the 18th century to the local fishermen, who learned to avoid them as the fishing nets would often be caught on these beachrock outcrops and tore apart. This is how the name Tegnùe originated: in the Venetian language it means "held back".

These natural "reefs" developed during the last 3000 to 4000 years thanks to the slow action of building organisms that live in a certain type of calcareous red algae of the Corallinaceae family. Tegnùe are found at depths of 15 to 40 m, and vary in size. The most far-reaching and well-known are those off the shore of Chioggia.

The variety of shapes of the outcrops, and their numerous chambers and ravines constitute a habitat fit for a varied ichthyic fauna: lobsters, gilthead breams, sea basses, cuttlefishes, rock fishes, crabs, corvines and shrimps. And all this is surrounded by the colours of anemones, sponges and sea-squirts. The basic role played by this ecosystem in the repopulation of the Upper Adriatic floor, as well as its extraordinary abundance, make this area, which has been declared a Biological Protection Zone, an underwater oasis of remarkable biodiversity.

There are many accredited scuba diving centres with local scuba guides organizing and accompanying scuba enthusiasts on diving adventures while ensuring safety, respect of the regulations, and protection of the oasis.