Water temperature in Finland

Finland's lakes and Baltic shores

Finland is a land of lakes. Päijänne, Pielinen, Kallavesi and Haukivesi are among the large waters of the Lakeland, with countless smaller lakes in between. Shallow lakes warm quickly in early summer and usually peak in July. Along the coast, Finland borders the Gulf of Finland, the Archipelago Sea and the Gulf of Bothnia, and the north stays noticeably cooler than the south. The summer season is short, yet many Finns keep swimming through winter in holes cut in the ice.

The 55 sites come from three sources. SYKE, the Finnish Environment Institute, measures on lakes and rivers, including Päijänne and Pääjärvi. Baltic readings come from buoys and coastal stations distributed by the Copernicus Marine Service, and these values are measured. Only two coastal spots use the Open-Meteo marine model and are labelled as model values. Given how many lakes Finland has, coverage is still sparse.

Municipalities test official bathing sites during the season, with ratings from excellent to poor under the EU Bathing Water Directive. In late summer, cyanobacteria blooms can spread in lakes and in the Baltic, and the water is best avoided then. On the coast, offshore wind can draw cold deep water upwards and drop the temperature within hours. On large lakes, wind builds waves quickly, and even on warm days the water below the surface stays cold.