Venice, June 14 - The first floodgate was installed Friday in the controversial water barrier under construction in the Venice lagoon. It was lowered in the Lido-Treporti waterway where the lagoon meets the Adriatic sea, which during high tide is prone to flooding the city. Conceived in 1984, the 5.7-billion-euro MOSE project is a series of retractable dykes in the straits around Venice. The deadline for implementing the gates is 2016, but the work is already reaching its endpoint, according to the Venice water authority The MOSE project, which in Italian is a play on the name for Moses, has been contested since its inception, both because environmentalists say it will interrupt the natural ecosystem and because some experts believe it will fall short of protecting the city. Italian heritage and conservation body Italia Nostra says MOSE will ultimately be "incapable" of halting dangerously high water and will have to be demolished soon after it is complete. Floods reached chest-high levels several times this fall and winter, flooding stores and ground-floor apartments. The causes are both natural and man-made. Decades of pumping groundwater caused significant damage to the delicate foundation before the practice was called off. Weather experts say the high-water threat has been increasing in recent years as heavier rains have hit northern Italy, probably due to climate change. Other possible explanations for the phenomenon include the sea floor rising as a result of incoming silt and gas extraction in the sea off Venice undermining the islands. According to a recent study, plate tectonics are also to blame as the Adriatic plate is sliding beneath the Apennine Mountains, causing the area to drop in elevation.