Päijänne Water Tunnel, 120-kilometre water tunnel in Southern Finland
The Päijänne Water Tunnel is an underground pipeline system that carries water from Lake Päijänne to the Helsinki region. The structure stretches 120 kilometers deep underground at depths between 30 and 100 meters, supplying drinking water to over one million people.
Construction began in the early 1970s and the tunnel officially opened in 1982. The project was created to address water supply problems in the Helsinki area, where local lakes could not provide enough clean water to meet growing demand.
The tunnel itself is not open to visitors, but the area around Lake Päijänne and nearby water treatment facilities are accessible. Information about the project is available at visitor centers and local museums throughout the region.
The flowing water is also used at a nearby hydroelectric power plant called Kalliomäki, generating about 7300 megawatt-hours of electricity annually. This dual use shows how the project generates energy while simultaneously supplying drinking water to communities.
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