Expanding the European water Framework Directive indicators to address long-term climate change impacts on lakes using mechanistic lake models

• Long-term monitoring data and predictive modeling anticipate key climate-related limnological change. • Simulations of physical and biogeochemical processes in lakes up to 2100. • By 2100, the deepening of the chl-a peak may not have a negative impact on the drinking water supply. • Warmer waters may progressively push suitable salmonid habitat deeper on both annual and seasonal scales. • Favorable temperature for embryonic development may not be reached after 2050 for intermediate and pessimistic scenarios. Climate change is altering lake ecosystems at an unprecedented rate, disrupting thermal regimes, biogeochemical cycles, and key ecological functions essential for human use such as drinking water, fisheries, and recreational activities. However, climate effects are often studied in isolation and over short time periods, which limits our ability to quantify the extent and speed of multifaceted ecological changes as well as our understanding of how lakes will evolve under climate change. We present a framework that integrates computer modelling, long-term forecasting, and multi-decadal limnological data to comprehensively evaluate 25 key metrics within the European Water Framework Directive related to lake functioning and ecological status through to 2100. Long-term projections of the effects of climate change were based on lake priority uses: 1) overall functioning, which supports aesthetic value and general attractiveness, 2) drinking water supply, and 3) stock of salmonids. Our findings reveal that although key thermal regime changes have already occurred, higher water temperatures will progressively push deeper salmonid habitat on both annual and seasonal scales. Favourable conditions for salmonids reproduction will exceed tolerance limits by 2050, and fishery management adjustments are needed. Conversely, drinking water supply should remain unaffected until 2100, assuming stable nutrient inputs and pollution levels. This approach offers a tool for forecasting climate change’s impacts on lakes, allowing decision-makers to anticipate measures to ensure long-term ecological and human benefits.