According to data available Wednesday, Lake Päijänne in Sysmä near Lahti would have been the best place for swimming enthusiasts to take the plunge, as its waters were warmest in the country.
Traditionally large bodies of water take a long time to warm up, but on Wednesday the water in Päijänne, the country's second-largest lake, measured 19 degrees Celsius – fully nine degrees warmer than the average for this time of year.
Other areas where water temperatures approached 20 degrees included Ali-Rieveli in Heinola just north of Lahti, Jääsjärvi in Hartola in the same region and Kyyvesi in Haukivuori, eastern Finland.
It’s not only in the south that lake waters are heating up; environmental officials say that waters are also heating up in northern Finland. For example, the water in Lake Kevo in the northernmost municipality, Utsjoki, recorded a temperature of 7.3 degrees Celsius, 3.3 degrees more than the average. Water temperatures at this location have been measured since 1962.
Seawater temperatures cooler
However water temperature readings in Lake Saimaa at Lappeenranta, south-east Finland, have been tested by officials for even longer than that – since 1916. According to Wednesday’s readings, those waters were 17.3 degrees Celsius – 6.4 degrees warmer than average for the time of year.
Lake water temperatures are automatically updated and the Finnish Environment Institute provides this information on its website (in Finnish). However the organisation points out that the readings are taken at one point and cannot be used for generalisations, especially for large bodies of water. The measurements are not validated manually.
The institute does not keep data on sea water temperatures, but the latest reading for the sea near Helsinki on Wednesday was 10 degrees. Temperatures were likely higher in sheltered areas.
