For the first time a system of 78 mobile floodgates has been tested in Venice, after years beset by delays and corruption.
The 1.5km (one-mile) Mose system of yellow dams was a “powerful project that has taken years to complete”, said Prime Minister Giuseppe Conte.
Venice was hit by the worst floods in half a century in November 2019.
Environmental protesters took to the lagoon on Friday, saying the barriers would damage the area.
Critics argue the sluice-gate system is 10 years too late. Work on the Mose project started in 2003, even though it was designed in the 1980s. It has gone three times over its original budget and resulted in the arrest of dozens of officials, the BBC’s Quentin Sommerville reports from Rome.
The coronavirus pandemic has brought tourism to a halt and stopped cruise ships from entering the lagoon but rising seas in the Adriatic continue to threaten Venice. Last autumn, more than 80% of the city was flooded.
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The prime minister and three government colleagues visited the control room on Venice Lido to see the 90-minute operation take place. “We are here for a test, not a parade,” he told reporters.
The four defensive barriers were raised and lowered at three inlets – two at the Lido, and at Malamocco and Chioggia.
Under the Mose (Experimental Electromechanical Module) system, if there is a very high tide, compressed air enters the 78 sluice gates and empties them of water, so they rise up and block the tide entering the lagoon.
Friday’s test lasted 90 minutes and officials said at full capacity the barriers could rise in half an hour. Elisabetta Spitz, the commissioner supervising the project, said it was not ready yet and would need another 18 months of testing.
Protesters from the No Mose group tried to disrupt the test but police stopped them.
“They had everything in the water, from police jet skis to dinghies, speed boats and coast guard vessels,” protest leader Tommaso Cacciari told Ansa news agency. “We tried to break the blockade but there was nothing we could do.”