About Paijanne Dam

Päijänne is Finland's second-largest lake and one of the deepest, reaching down to 95 metres in places within the Central Finland and Päijät-Häme regions. The lake stretches nearly 120 kilometres from north to south and drains via the Kymijoki river into the Gulf of Finland. Regulation for hydroelectric power production began in earnest after 1964 and is managed through a series of dams and weirs on the Kymijoki. With an estimated water volume of 4,000 million cubic metres, Päijänne is the primary drinking water source for the Helsinki metropolitan area, supplied through the Päijänne Water Tunnel — at 120 kilometres the longest rock tunnel in the world. The tunnel was constructed in the 1970s and 1980s and delivers up to 18 million litres of water daily to over one million people. The lake's regulated water levels are carefully managed to ensure adequate tunnel inflow while protecting shoreline ecosystems and the livelihoods of fishing communities. Päijänne is also a popular summer destination for sailing, kayaking, and cottage tourism.