The global demand for desalinated water is increasing at a remarkable rate. In a future with increasing demand for water and low-carbon electricity, an interesting ecological dilemma emerges. In a decarbonized world, providing desalinated water for domestic use and aquatic ecological restoration could increasingly come at the expense of open space lost to renewables such as solar photovoltaics (PV) and wind turbines. In this article we examine the environmental tradeoffs of providing freshwater from desalination under a solar photovoltaic-based decarbonization strategy, using Israel as an example. Israeli policymakers are tasked with finding an acceptable balance between reducing CO2 emissions, increasing water supply for human consumption, preserving open space, remediating aquatic ecosystems, and aiding Palestinian and Jordanian neighbors in efforts to mitigate the risks associated with acute water shortages. We simulate future 2050 ecological tradeoffs from large-scale desalination in Israel under a “business-as-usual”, a “nature-matters”, and a “nature-and-cooperation-matter” scenario. We find that the solar PV required for generating electricity for desalination alone could take up an area more than half the size of Israel’s second-biggest city, Tel Aviv. The marginal impact of an additional loss of 37km2 of open space is difficult to predict, but if ecological corridors or critical habitats are affected, it could be catastrophic for many stressed species and ecosystems across Israel.