Continued retreat and disappearance of glaciers cause fundamental changes in cold mountain ranges and new landscapes to develop, and the consequences can reach far beyond the still ice-covered areas. A key element is the formation of numerous new lakes where overdeepened parts of glacier beds become exposed. With the first model results from the Swiss Alps around 2010 of distributed glacier thicknesses over entire mountain regions, the derivation of glacier beds as potential future surface topographies became possible. Since then, climate-, water-, and hazard-related quantitative research about future lakes in deglaciating mountains all over the world rapidly evolved. Currently growing and potential future open water bodies are part of new environments in marked imbalance. The surrounding steep icy slopes and peaks are affected by glacial debuttressing and permafrost degradation, with associated long-term stability reduction. This makes the new lakes potential sources of far-reaching floods or debris flows, and they represent serious multipliers of hazards and risks to down-valley humans and their infrastructure. Such hazard and risk aspects are also of primary importance where the lakes potentially connect with hydropower production, freshwater supply, tourism, cultural values, and landscape protection. Planning for sustainable adaptation strategies optimally starts from the anticipation in space and time of possible lake formation in glacier-covered areas by numerical modeling combined with analyses of ice-morphological indications. In a second step, hazards and risks related to worst-case scenarios of possible impact and flood waves must be assessed. These results then define the range of possibilities for use and management of future lakes. Careful weighing of both potential synergies and conflicts is necessary. In some cases, multipurpose projects may open viable avenues for combining solutions related to technical challenges, safety requirements, funding problems, and societal acceptance. Successful implementation of adaptive projects requires early integration of technical-scientific and local knowledge, including the needs and interests of local users and decision makers, into comprehensive, participatory, and long-term planning. A key question is the handling of risks from extreme events with disastrous damage potential and low but increasing probability of occurrence. As future landscapes and lakes develop rapidly and are of considerable socioeconomic and political interest, they present often difficult and complex situations for which solutions must be found soon. Related transdisciplinary work will need to adequately address the sociocultural, economic, and political aspects.