Tegnue (singular tegnua) are rock formations which have developed in the sea bottom of the Gulf of Venice, in the northern Adriatic Sea. They are bio-sediments which are very similar to coral reefs and for this reason they also are called Adriatic coral reefs. They are found especially off the coasts of Caorle, the Cavallino peninsula, the Lido di Venezia island and the Sottomarina peninsula at Chioggia. There are eight such formations. They are at a depth of -15/-40 m. The largest formation is off the coast of the Cavallino peninsula.