Päijänne

Päijänne is a large freshwater lake in southern Finland. By surface area it is the second largest in the country, covering about 1,080 square kilometers. The lake extends roughly 120 kilometers from north to south and reaches depths of up to about 95 meters. It is bordered by numerous municipalities in the Päijänne region and parts of Central Finland and Uusimaa, making it a defining feature of the southern Finnish lakeland. The lake is part of the Kymijoki basin, with its outflow via the Kymijoki River toward the Gulf of Finland.

Hydrology and infrastructure: Päijänne receives inflows from many smaller rivers and streams and is regulated by weirs and dams to support flood control and water supply. A major feature is the Päijänne Water Tunnel, completed in the early 1980s, which transfers drinking water from Päijänne to the Helsinki region; the tunnel is among the longest of its kind in the world.

Environment: The lake has clear boreal water and supports species such as pike, perch, rudd, roach and brown trout, among others. Its shores host mixed forests and numerous islands and peninsulas, contributing to a diverse aquatic and terrestrial habitat.

People and economy: Päijänne is a popular site for boating, fishing, sailing and cottage holidays. The surrounding area includes small towns, resorts and nature trails. The lake’s water quality and accessibility help sustain Helsinki’s drinking-water supply and regional tourism.

Conservation and management: The lake is managed for water quality, fisheries and recreation, with protected areas and nature reserves along parts of its shoreline.