Lake temperatures have plunged in Finland. Hydrologist Johanna Korhonen of the Finnish Environment Institute (SYKE) says that water surface temperatures in eastern and central Finland have dropped by as much as four degrees within a few days.
A spell of hot weather in late May and early June quickly raised temperatures to unseasonably warm levels, but in recent days cool winds and rains and chilly nights have brought them back to below 20 degrees Celsius throughout the country.
Fluctuations common in June
“In early summer, the warm surface level of lakes is usually very thin,” explains Korhonen. “It’s typical for them to become very warm but then to cool off again as the winds change direction and weather changes.”
Towards the end of summer, lake waters warm up more thoroughly and are no longer so strongly affected by winds. In fact, winds mix the water within lakes more thoroughly so that their overall temperature stabilises.
Lake water temperatures remain just below the 20-degree mark at SYKE measurement points in the Päijät-Häme region. At Ala-Rieveli in Heinola, it was at 19.8 degrees on Thursday, while Lake Päijänne was just under 19 degrees at Sysmä.