There are millions of lakes in Europe, providing key ecosystem services for society, ranging from drinking water and food to transportation and recreation. Yet, these lakes are highly vulnerable to climate change, particularly the observed increase in the frequency and severity of extreme heat events in recent decades. A numerical modelling study demonstrated that one such event, the 2018 European heatwave, had a considerable influence on lake ecosystems across the continent, with mean and maximum lake temperatures being 1.5°C and 2.4°C warmer than average. The model results also demonstrated that by the end of the 21^st century, the lake temperatures that occurred during the heatwave of 2018 will become increasingly common. The impacts on lakes to these heat extremes are likely to be widespread and persistent, with aquatic organisms being pushed to the limits of their resilience.