Frozen Masurian lakes. Is an icy surface good news?

A surprisingly frosty start to January has meant that even the largest Masurian lakes are now covered with ice. Smooth surfaces have delighted fans of ice skating and hockey, while putting rescue services on high alert, as bravado and irresponsibility make accidents on ice all too easy. How are fish coping in this situation?

Masurian lakes covered with ice

Standing water in ponds and lakes freezes much faster than rivers flowing with a strong current. As early as last week, the Polish Press Agency reported that all Masurian lakes had become ice-covered, warning that the ice was still too thin to risk walking on. Lake Niegocin froze last, as wind had consistently broken up the surface for several days, making it difficult for the ice to consolidate.

Earlier, ice formed on lakes Mamry and Śniardwy, where nighttime air temperatures dropped to as low as minus 20 degrees Celsius. According to Stefan Świderski, head of the Masurian Water Rescue Service station in Okartowo, the growth of ice thickness on Poland’s largest lake was hindered by a layer of snow acting as insulation. On Saturday, 10 January, the rescue service reported that ice thickness in Chudzicka Bay had reached 12 to 17 centimetres, but numerous frozen cracks were visible on the surface.

Ice is also plentiful on smaller Polish water bodies. The Nagoplańskie Water Rescue Service in Kruszwica reported on Tuesday that the ice cover in the middle of Lake Gopło was 15 centimetres thick.

Ice on lakes and nature

The Masurian lakes are one of the most environmentally valuable regions in Poland. Does an ice cover pose a threat to organisms living in these waters?

Experts from the Centre for Water Monitoring and Protection at the University of Gdańsk reassure that lake ice formation is part of the natural process of seasonal change in aquatic ecosystems. An ice layer on the surface of a water body has many positive aspects. It protects underwater organisms from sudden temperature fluctuations and reduces light penetration, which slows biological processes and facilitates winter dormancy.

More concerning for nature is the shortening of the ice season caused by climate change. As a result, water temperatures rise more rapidly in spring and summer, leading to stronger and earlier algal blooms, changes in food web structure, and shifts in species migration.

Fragile ice, fragile life

For several days now, the Masurian Water Rescue Service has been running an intensive series of talks in schools and community centres. Rescuers explain how to behave on ice and when to avoid it altogether, and they also provide guidance on basic self-rescue and rescue techniques in the event of ice breaking. This is knowledge well worth actively seeking out.

County police headquarters also warn online about the dangers of entering frozen lakes, rivers and ponds. According to the Prevention Office of the National Police Headquarters, safe ice cover should be at least 10 centimetres thick. However, the specialised Search and Rescue Service from Świebodzin reminds that ice thickness is usually highly uneven, and local conditions are influenced by factors such as water depth, inflows and outflows, and temperature fluctuations. When a layer of snow is present, the actual load-bearing capacity of ice may be 10 to 30 percent lower than that of clear ice, according to the Water Rescue Service in Gołuchów.

Stepping onto ice near the shore of shallow lakes may at worst result in soaked clothing and a cold, but venturing further out can cost lives.