Quabbin Aqueduct
The Quabbin Aqueduct carries water from the Quabbin Reservoir to the Wachusett Reservoir. It is part of the Eastern Massachusetts public water supply system, maintained by the Massachusetts Water Resources Authority (MWRA). At 25 miles (40 km) in length, it is one of the longest aqueduct tunnels in the world.
Tunnel data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).