Beneath the Catskills, a mountain range in upstate New York, lies the Delaware Aqueduct, a massive underground tunnel that supplies drinking water to New York City. This 85-mile-long tunnel, completed in 1944, delivers about 600 million gallons of water daily to the city’s eight million residents using gravity. The aqueduct was built during World War II and designed to last for decades. However, since 1988, it has been experiencing leaks, with initial estimates suggesting up to 136,000 cubic meters of water were lost each day. These leaks were traced to cracks in the limestone surrounding the tunnel, first confirmed in 1990 and 1992 near the towns of Roseton and Wawarsing. To address the leaks and prevent potential water loss, engineers began constructing a bypass tunnel in the early 2000s. This 4-kilometer-long tunnel, located about 600 feet below the Hudson River, is designed to divert water around the damaged section of the original aqueduct. The project has taken over two decades and cost about $1.5 billion. Recently, the northern section of the Delaware Aqueduct was closed in September 2024, allowing the final connection between the old and new tunnels to begin. However, the project was paused in November 2024 due to a historic drought, which made it too risky to drain additional water from reservoirs. The Delaware Aqueduct was built with reinforced sections to withstand potential wartime damage, but it was never intended to last more than a few decades. Engineers opted for the bypass tunnel rather than shutting down the original aqueduct, which would have cut off a significant portion of the city’s water supply for months. The new tunnel includes two deep shafts, one 210 meters and the other 275 meters deep, allowing workers to access the underground structure from the surface. The final step in the project—connecting the bypass tunnel to the original aqueduct—is the most delicate. It requires draining the old tunnel to weld the two structures together while monitoring the risk of collapse. The leaks in the original tunnel, though problematic, had helped maintain the integrity of its lining by applying external pressure. Without that pressure, the risk of collapse increases significantly. Despite the delays caused by the drought, the project is now expected to be completed in 2027, nearly 40 years after the initial cracks were discovered.